“unicorn hunters” are a well known trope and generally looked on with scorn within ethical non-monogamy / polyamory communities. They’re almost always a bad kind of hierarchical, and usually don’t see the new third person as an equal, whole, person.

I’m going to guess that bisexual men looking for another man are slightly less likely to be this particular kind of dehumanizing, but I don’t have any data to back it up.