After the fat Buu expelled evil from himself, it coalesced into a skinny Buu that went onto to absorb the other, forming "Super" Buu, a tall, skinny and intelligent Buu capable of complex speech ...

There isn't any reason the two shouldn't share Buu's ability to absorb other fighters and, specifically, to absorb alternate versions of themselves. Even if Majin Duu cannot defeat Tamagami 1 ...