+1 to what Count Adhemar said.
If the GK FAQ lists Mandrakes then it clearly covers units from Codex: Dark Eldar so, since it doesn't say that Khymerae are daemons, presumably it's safe to infer that they're not.
(p.s. This should be under rules queries rather than tactics I think - I expect it will get moved.)
Thou expecteth correctly, moving to Rules Queries & Questions. Gob.