My brother was born deaf, so I have used ASL to for over 30 years. I think it's a good idea but like a few people mentioned, there can be some issues. Even though the basic signs don't change, a lot of people that use ASL have made up there own signs. It is good between a small group but I'm not sure about it's use in a broad manner such as the universal dive signs that we are taught.
Two examples....when my brother left Texas for college in Rochester, NY, I could understand him. Upon his return, it was like I talking to someone from another country. Had to have him spell everything out!
Some of the standard signs for ASL could get confusing. The sign for "lie" is a your palm flat moving across your chin, and it you want to say "lie, lie, lie" then you'd move it rapidly back and forth across your chin. Move your hand off your chin down to your throat, doing the same motion, you've now got a diver giving a signal which could look like an OOA signal!
Diver 1..."damn, out of air"....give signal to buddy using standard dive signals
Diver 2 sees Diver 1 give signal...he's calling me a liar, screw him...let that shark eat him!