First, looking at the BoardGameGeeks page for this, I noticed cards taking place in The Inner Sanctum (presumably of Silver Twilight Lodge). Now either thats for combining or FFG is using the same locations which is cool too.
The Silver Twilight Lodge and it's associated Inner Sanctum are part of HP Lovecraft's Mythos. Both AH and MoM are set in that universe, so it's hardly a surprise that they will share some of the same places, people and Things. That doesn't mean the games will be mechanically compatible. Look at Descent, Runebound, Runewars and DungeonQuest. They all share the same universe, they all mention at least a few similar places, people or items. None of them are mechanically compatible with one another (although there are certainly fans who work ravenously to build house rules for that purpose.)
My other guess is because the miniatures seem to have a AH monster chit sized slot in the bottom!
Without knowing the mechanics of MoM it's hard to say why that hole is there. I agree it looks like it would fit an AH monster token nicely, although I don't see any holes on top for the sneak check and other info one normally needs to see during play. I haven't seen a good shot of the bottom of the base to see if it's hollow and you could read the backside of the token through there.
Personally, I think sliding the monster token in there would be somewhat pointless if I had to keep pulling it out again to check info on one or both sides. Worse than just playing with the token normally. Of course, if there are appropriate holes on both sides and I just can't see them in the photos I've seen, that would resolve that concern.
Regardless, it's entirely possible that the slot serves a purpose in MoM mechanics and the fact that an AH monster token fits in there is purely coincidence. All FFG tokens (of which there are a great many in most games) have a uniform thickness. The AH monster tokens are roughly 1 inch square, which strikes me as a farily common size for square tokens in general. Maybe it's not intentional, that's all I'm saying. Without knowing how the MoM rules work, it's hard to say why that slot is there.