I keep them in the same room. My boas are in separate enclosures(boaphile cages). My ball pythons are in racks.
Just me, but I wouldn't use back heating with boas. My ball python racks use back heating. My boa cages have UTHs.
IF they are quarantined for appropriate time span; healthy-looking and -acting boas from reputable breeders get 30 days QT, ones with unknown genetics or that show any signs of illness get 4 months at my house
The reason why many people believe in separating boas and pythons is because there have been studies showing that boas might be natural carriers of IBDV. This has not been confirmed and these studies have not been released (to my knowledge ), so basically these are just rumors. But even so, wash hands thoroughly after handling a snake and keep a VERY close eye out for any symptoms of IBDV.