I have never had a problem with driftwood and ammonia. Is the wood rotting anywhere that you can tell? Where did you find it. It could be possible that some kind of burrowing insect used it for a home but I still don't think that would cause an ammonia spike.
hum my tank was ready ammonia 0 and nitrite 0 and nitrate 10, for a week before the wood.
now ammonia went from .50 to 1ppm and the nitrite is 0 and nitrate is 5, I thank the plants for the nitrate of 5. I will clean out the tank, there maybe some dead food or plants.