You are obviousely taking this very serious.
As for me, everyone can handle this as he likes. Just wanted to throw in a quote from the rules that matched the thread.
Having said this, I will now pretend taking this question serious and put an answer to your post:
Myself, the last time I played Warhammer was back in the eighties

.
But as much as I am concerned, the Worlds of Warhammer and of Heroquest are
not identical. The Heroquest figures were created by Games Workshop, and they just used the background they had got, so there are some similarities. But how would you integrate the reign of Morcar/Zargon in the Warhammer history?
To cry out loud, Warhammer Orcs reproduce by spores... I don't want my valliant Heroes fight against mushrooms!

The Fimir race was discontinued in Warhammer, anyways.
You may think otherwise, but even then there are differences how a race is handled in different publications of the fantasy genre, even in different editions of Warhammer itself.
The primary source of data about the Heroquest Fimir should be the Heroquest rulebook, not some other game. And being clearly humanoid in stature, when the Heroquest rulebook describe them as "lizardlilke", they are lizardmen. What else?
A strange flock of lizardmen, of course, beeing one-eyed and all - leaving still room for other races...
