Nikkoku never includes okurigana in headwords (i.e. it doesn't even have the 抜け道 form). Similarly, Shinmeikai always includes a form without okurigana, regardless of whether it's used or not. I don't have access to Oukoko or Iwakoku but I suspect they have the same policy. We typically use Daijrin and Daijisen as a guide to what forms are standard/irregular; in this case, neither of them has 抜道.

Is it irregular, though? shinmeikai, nikkoku, oukoku, and iwakoku have it.

nikkoku also has 抜路, which is just about as common as 抜け路

Google N-gram Corpus Counts
175,893	 95.9%	抜け道
  1,202	  0.7%	抜道
    128	  0.1%	抜け路
     72	  0.0%	抜路
  6,038	  3.3%	ぬけみち

@@ -9,0 +10,3 @@
+<keb>抜道</keb>
+</k_ele>
+<k_ele>
@@ -10,0 +14,4 @@
+<ke_inf>&rK;</ke_inf>
+</k_ele>
+<k_ele>
+<keb>抜路</keb>

gg5, ルミナス

I think we can drop 抜道. Irregular and uncommon.

@@ -8,4 +7,0 @@
-</k_ele>
-<k_ele>
-<keb>抜道</keb>
-<ke_inf>&io;</ke_inf>
@@ -27,0 +24 @@
+<gloss>shortcut</gloss>
@@ -32,0 +30 @@
+<gloss>way out (of trouble)</gloss>

抜け路 (ぬけみち) is in daijs

Google N-gram Corpus Counts
175,893	 96.0%	抜け道
  1,202	  0.7%	抜道
    128	  0.1%	抜け路
  6,038	  3.3%	ぬけみち

@@ -10 +10,2 @@
-<keb>抜け路</keb>
+<keb>抜道</keb>
+<ke_inf>&io;</ke_inf>
@@ -13,2 +14,2 @@
-<keb>抜道</keb>
-<ke_inf>&io;</ke_inf>
+<keb>抜け路</keb>
+<ke_inf>&rK;</ke_inf>

gg5, prog, nc

@@ -10,0 +10,3 @@
+<keb>抜け路</keb>
+</k_ele>
+<k_ele>
@@ -11,0 +14,1 @@
+<ke_inf>&io;</ke_inf>
@@ -19,0 +23,8 @@
+<gloss>byway</gloss>
+<gloss>bypath</gloss>
+<gloss>byroad</gloss>
+<gloss>secret path</gloss>
+<gloss>way of escape</gloss>
+</sense>
+<sense>
+<pos>&n;</pos>
@@ -20,0 +32,1 @@
+<gloss>excuse</gloss>

I don't think "loophole" completely captures the meaning of this word.  It also can mean more of a generic "a way out (of someplace or something)", perhaps with a connotation of cleverness or secrecy.  In ordinary use, I only ever hear "loophole" in reference to a contract or similar agreement, but I've seen "抜け道" used to denote an exit, secret passage, etc.

Koj, Daijr/s, etc.

Trimming considerably. The proposed version was too complex and detailed.

@@ -25,2 +25 @@
-<gloss>traversing the length of one or more swords barefoot, edge up ( acrobatic stunt )</gloss>
-<gloss>sword-walking (barefoot. oft. in reference to Shinto ritualistic ascent of a ladder of sword blades)</gloss>
+<gloss>walking barefoot on the edge of a sword blade (acrobatic stunt)</gloss>

I'll just cut the fire-walking xref preemptively. It would be nice if these two paired Shinto rituals, performed for similar purposes, could be tied together, but the fire-walking xref is generic, so this doesn't really work anyway.

@@ -24 +23,0 @@
-<xref type="see" seq="1724530">火渡り・ひわたり</xref>

Video of combined fire walking, sword-ladder-climbing ritual.  
神事　火渡り　刃渡り
https://www.youtube.com/watch?v=VREpjBFZVAM

Lots of pictures, modern execution of the ritual
刃渡りを (2007/05/08) の記事画像
https://ito3382.exblog.jp/iv/detail/?s=6037241&i=200705/08/75/c0009475_22332188.jpg

Long writeup on the practice of sword and fire walking as Shinto religious/miracle practice.  Illustration with a ladder.
https://www.touken-world.jp/tips/32730/

(This is a chapter in a book, a 40-page narrative 1st-hand account of witnessing the ritual)
"Occult Japan; or, The way of the gods; an esoteric study of Japanese personality and possession"
https://en.wikisource.org/wiki/Occult_Japan/Miracles
We now come to the third miracle of the three ; the Tsurugi-watari, or the Climbing the Ladder of Sword-blades.
...
Evidently this was the material means to the miracle, for against it a ladder with notches suggestively vacant of rungs, led up to a frail plank platform raised astonishingly high into the air. We had somehow assumed that the sword-walking took place on the flat, and not, as it appeared it was to be done, skyward.
...

剣の刃渡り（つるぎのはわたり） の意味・使い方
https://dictionary.goo.ne.jp/word/剣の刃渡り/
刀の刃の上を素足で渡る曲芸。転じて、きわめて危険なことのたとえ。かみそりの刃渡り。
「我輩の生涯は―だから」〈魯庵・社会百面相〉

刃渡り
２ 刀の刃の上を素足で歩く軽業 (かるわざ) 。

This form includes the religious reference:
かたな【刀】 の 刃渡(はわた)り
刀の刃の上を渡り歩く曲技。社寺の境内などで山伏や行者がやって見せて剣難よけの守り札を売った。
daijs:
刀の刃の上を人が渡り歩く曲技

nikki は‐わたり【刃渡】
② 刀剣の刃の上を、素足でわたり歩く軽業。


With picture of acrobatic stunt walking blades lengthwise.
http://no-sword.jp/blog/2010/08/tsurugi_watari.html
In ancient times, walking on swords was a Shinto ordeal called Tsurigi Watari [sic!]. However, after Japanese conjurers learned the secret, the Shinto priests abandoned the rite. Later, Far Eastern performers brought the feat to Western audiences (Gibson 1967, 91). Resembling a stepladder consisting of five to seven rungs of broad swords placed edge upward, the ladder of swords is a sideshow mainstay.

Other terms:  剣渡り(つるぎわたり) 剣の刃渡り　（つるぎのはわたり) 　刃渡り神事

This term is evidently [news1] because it is a common way to report the length of knives/blades used in crimes.

The $64k question: are 剣渡り, 剣の刃渡り, 刃渡り, and 刀の刃渡り different things.  In modern use, at least, it doesn't *seem* like it.

daijs does identify explicitly as barefoot, and as a feet of acrobatics.  no-sword.jp references a historic sketch where an acrobat performs in tabi(socks), lined with something protective. (so, as a cheap acrobatic performance, even "barefoot" would not seem to strictly be required, though this disagrees with the kokugo).  

dictionary entry aside, 剣の刃渡り is actually best known as the name of a particular mountain peak, where there is a particularly long, narrow peak one must cross, with the possibility of falling from either side if careless. (this is all google will find if you search, many hits) 
https://souraku.jp/home/newpage424html.html

Apparently a successful Japanese ballplayer practiced 刃渡り as a means of training... Also included firewalking
https://yakyutaro.jp/r.php?hash=d71AE
“刃渡り”のほか、火が残る炭の上を歩くという“火渡り”まで練習に取り入れ、精神力を鍛えてきたというから、恐れ入る。
https://www.asahi.com/articles/ASQ3X6RLJQ3RPTIB00F.html
精神修養のため、2本並べた日本刀の刃の上を素足で歩く「刃渡り」を実施。

2本並べた日本刀 ... is 並べた end-to-end, or side by side? I imagine side by side, one foot on one blade, one on the other?

@@ -24 +24,4 @@
-<gloss>walking on the edge of a sword</gloss>
+<xref type="see" seq="1724530">火渡り・ひわたり</xref>
+<misc>&rare;</misc>
+<gloss>traversing the length of one or more swords barefoot, edge up ( acrobatic stunt )</gloss>
+<gloss>sword-walking (barefoot. oft. in reference to Shinto ritualistic ascent of a ladder of sword blades)</gloss>

@@ -11,0 +11,1 @@
+<ke_inf>&io;</ke_inf>

daijr daijs
ALC

@@ -19,1 +19,4 @@
-<gloss>length of a (sword) blade</gloss>
+<gloss>length of a blade (sword, knife, etc.)</gloss>
+</sense>
+<sense>
+<pos>&n;</pos>