Polygamists are not adopting, or they are? Has that gone somewhat mainstream?
Does the law support it?
Of course they do — divorcees aren’t forbidden from adopting, and if someone remarries a few times, that makes them a (what) in all but name ….?
Plus quite a few people probably have unofficial arrangements that are polygamous in all but legal name. If those can be hidden from a background check, then I’m sure some of them do adopt.