In SoulMS, Zak, Pap, Scar/Targ and BG are all summonable and you enter their maps in the same manner. In that sense, no, BG isn't gMSlike.
At face value, the only distinguishing factor between BG and all the other ones listed above is that you can't buy combs from the NPC you click to get in - you can only get them from Anego. Coding-wise, there might be something, but it certainly doesn't seem like it.