I think an Alpha-style "classic" werewolf is totally legit as a host, since they definitely take wizards, sorcerers, & other practitioners, and a "classic" werewolf is still human-with-powers.
Actually, I think it's pretty broad. Harry certainly thought in SmF Thomas could be possessed - he warned him about touching the coin, "it could let you touch Justine again". Admittedly Thomas is very much an outlier among WCVs, but if he has enough free will it should be possible for Red Court Infected, Changelings, etc. who have at least as much. I think the Fallen gets a choice, though - it might well simply refuse to possess someone like Madeline(? - the really out-of-control Raith who gets burned and fed on by Lara). OTOH, it could probably do more even in that kind of host than stuck in the coin - especially since it'd probably be strong enough to overwhelm the White Court phage. Possibly a WCV/Denarian (or Red Court Infected/Denarian, etc.) would be functionally a Denarian, the other side suppressed, but if they ever rejected the coin it would be "un-suppressed".
And we do have a canonical case of "double possession", though not involving a Fallen - Madrigal, who already had a White Court demon/phage, is possessed by an Outsider in WN. So maybe the powers would 'combine'/merge/work together as they seem to have done in that case, creating a really terrifying Denarian.
Anything truly not human - fae, Red or Black Court Vampires, ghouls, etc. - is distinctly off limits though.
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The really interesting question is what happens if the Winter Knight touches a coin? I'd imagine Mab goes "MINE!" and burns the Fallen shadow right out of the Knight's head, but who knows?