@@ -12 +12,2 @@
-<gloss>hetaira (ancient Greek prostitute)</gloss>
+<misc>&hist;</misc>
+<gloss>hetaira (prostitute in ancient Greece)</gloss>

The リーダーズ+プラス (EJ) dictionary has ヘタイラ as one of the Japanese glosses of hetaera, so I'm prepared to accept it as a Japanese term, albeit rather rare.
Other glosses were 教養ある遊女, 高級娼婦, めかけ, 売春婦

I think that it should be there for the same reason that it's in English dictionaries. (e.g. https://www.merriam-webster.com/dictionary/hetaera). There are plenty of hits on Google. Where do you draw the line at what is a "true word" or "merely a transcription." Is エレベーター also not a word? 

Encyclopedias are a compendium of knowledge. An encyclopedia would explain what everything about hetairai and their history, as Wikipedia does. We don't do this. I briefly glossed the word, as might be done in an English dictionary, because it might be unfamiliar to many readers. This is a far cry from an encyclopedic entry, which would be at least a hundred words.

As for using Wikipedia as a sole source, I usually also do a search on Google. If a word has an entry on the Japanese Wiki, it's a good indication that it has a certain degree of notability. I find that Wikipedia is usually a reliable source.

The latter, in my view. 

It's one of the reasons I'm sometimes reluctant to approve entries that only cite Wikipedia as a reference.
JMdict isn't an encyclopedia.