I disagree on adding it to William's page given it's non-canon status, even if it IS meant to be him (which i am not completely opposed to). William's main page should be main continuity stuff, adding a non-canon, barely indexable form to it would just make it messier
I don't think Burntrap's identity really matters at this point, he has been reduced to Gregory's vent OC in canon, but there is strong evidence for both of them. He hits the Mimic arm pose, he has an arm where William didn't (last we saw)... But he also has fleshy bits and is styled after Afton. Really, it could be both, could be neither, shouldn't matter nowadays lol