I'm not practiced in either, but I'll throw some thoughts out there:
A) If you're unable to actually practice the snatch, then it doesn't really matter what exercises might have carryover to it. It's not something you can expect to not suck at, because you did exercises that are supposed to carryover.
B) There's almost certainly less carryover than there is with the exercises weightlifters typically use to improve their snatch
C) I imagine there's some of the same benefits, in that they're both an explosive pull. But I suspect the DB snatch doesn't live up to the real thing. Personally, if I wanted to do an explosive pull, and olympic lifts aren't being considered, I'd do speed deads.
D) Perhaps more important, is what is the end goal? What is it that you'd want to get out of doing either lift? Because maybe the DB snatch is reasonable for this goal, or maybe there's a better option.