DeDeDe is definitely one of Snake's hardest fights. The chaingrab OWNS snake, and Snake gets completely gimped by DeDeDe's edgeguard game. Seriously, I've been taken from zero to gimp off of one DDD grab. It's hard to avoid his grabs, too, because their range is broken.
I actually feel like Snake has the advantage on stage if he can play a good enough game of keep away. Snake outcamps pretty hard, and outranges D3 with both tilts and aerials. That is, of course, until DDD gets a grab and ***** you. Don't mortar dash towards him unless he's right on top of you. If you let him react, you'll get grabbed by a good DDD player.
If the stage has platforms, try to get a prox. mine on it, so that DDD chaingrabbing you will activate it and knock you out of it.
One thing, do NOT plant C4 on stage. You'll need it to avoid the gimp.