If you've got diggers like eartheaters or worse, you'd just want it to be secure enough to not topple onto them. Otherwise, the driftwood--properly treated--shouldn't really affect your PH, and so it's a matter of taste.
I have a large piece in with some CA live-bearers that would look more natural with rocks, but then again, I have neons & otos, too. Purity challenged, I am.