32bit COM should work fine in 64bit Windows since it can run 32bit software - even classic VB. Obviously that would require a 32bit runtime. For a 64bit runtime they'd need either a 64bit version or only able to load 32bit out of process COM servers. AFAIK most COM stuff for VB was in-process (e.g. ActiveX controls) so those might be a problem but perhaps some sort of "32bit-to-64bit" bridge (via a separate 32bit process that communicates with the 64bit runtime) would work for the most part.

I think a harder part would be libraries/COM/extensions/whatever that access/modify the VB6 runtime internals.