Here is the frequency info, according to the OED:
omophagist, 1 cite, frequency band (FB) 1
nidor, multiple cites, FB 2
opsigamy, 2 cites, FB 1
opsimathy, multiple cites, FB 2
merkin, many cites, FB 2
agelast, 4 cites, FB 2
exsibilation, 3 cites, FB 1
vagitus, 6 cites, FB 2
dactylonomy, many cites, no FB given
lapidate, 5 cites, FB 2
boanthropy, 2 cites, FB 2
FB 2: < 0.0099 per 1 million words; 45% of the words in the OED are FB 2
FB 1: no frequency given, but the pattern would be < 0.00099 per one million words, 18% of the words in the OED
The frequency bands are very wide, so a word at the top end of one band would be ten times more common than one at the low end. It’s only the grossest of comparisons.
Omophagist is the only one of these that the OED actually marks as obsolete; this may change as these entries are updated, but most have relatively recent citations.
Merkin is the only one on this list that I’ve seen in the wild. It’s probably at the top of FB 2, far more common than the others listed here.
Dactylonomy has shifted in meaning; it now refers to the study of fingerprints, and is rather common in such technical discussions.
Nidor is a borrowing from Latin, as opposed to being formed in English from classical roots, and that may account for it being used a bit more than the others.