Peckoltia will rasp some wood. Otocinclus, bristlenose, and common's don't "REQUIRE" driftwood, but they will definitely be seen chewing on it, if it's available. Driftwood is definitely going to affect your pH, depending on the age of the piece and the level of tannic acid still left in it to leach out. If you're having to add coral to the tank to maintain a stable pH, you probably wouldn't want to add a large amount of driftwood. A few small pieces, enough for most any pleco to get the lignin from the wood, would probably be safe, even with very soft water. Just make sure you're doing regular partial water changes to combat the softening process.
Barbie