First off, both of these monkeys have girlfriends. You find out Salsa's in the Death Desert later on in the game, and you find the Bubble Monkey's after you get through with Jeff's Solo Part. Or, mainly through there. Another thing is that they both have a major role in the game. The Bubble Monkey helps you, and if he didn't, the game wouldn't have continued on. Salsa also plays a major role in the game, as a playable character and major supporter.
The Bubble Monkey only appears in Earthbound, and will appear in a video in Mother 3 as a cameo. He gets married to his girlfriend sometime before Ness and company go to Dr Andonuts' lab to fix the Sky Runner