True, our audiences are somewhat different, but we obviously have plenty of Japanese users (through weblio, etc.) as well. 
I'm sure J-E translators also appreciate GG5 including a wide register of translations, see
https://www.japantimes.co.jp/life/2015/09/21/language/translation-gets-tough-bow-green-goddess/
"When translation gets tough, bow to the 'Green Goddess' [...]
WWWJDIC offers “interesting” and “amusing,” but the Green Goddess devotes half a page (in very small font) to examples, 
including “pleasant,” which fits better in the context of this essay"

@@ -16 +15,0 @@
-<gloss>rat</gloss>

I think that's because JEs like GG5 also cater to Japanese native speakers who are writing in English and are therefore concerned about register. The colloquial/derogatory glosses are always tagged as such.
I don't think we need to do that here. "Rat" is unlikely to be a helpful gloss to the sort of people who use jmdict (Japanese learners and J->E translators).

chujiten has "squealer" and "grass"

In general, I think it's alright to include 
translations that don't perfectly match the 
register of the original word, esp. when 
there's several other glosses and the 
offending translation is among the last 
glosses. I find this is how gg5 and chujiten 
do it too?

I don't think it's needed. It's a colloquial and derogatory term, unlike 密告者.

@@ -15,0 +16 @@
+<gloss>rat</gloss>