I've also noticed different, mainly Visayan, fighting arts claiming to know, in addition to their native daggers, sticks, bolos, etc., how to use a weapon such as the Kampilan or barong.
Well, IMVHO the key word here seems to be "claiming (to know)" - AFAIK it's quite often 2nd/n-th generation practitioners enthusiastically embracing well-known Moro weaponery rather than the widely-respected style founders and their direct long-time students...
In my experience, a garab is a completely different animal than, say, a barung. And from what little I've been able to glean, these 2 blades are employed very differently. There are enough sleek folks around and I wouldn't want to be on the receiving end of just about anything they might pick up! However, there's still a fundamental difference between making something work and studying a traditional "tool" of any good MA system...
BTW, I still have to see any antique kerambit from the Philippines. Obviously, there are also "fashion" influences in MA circles...