I've never heard of it, and it doesn't make much sense to me. Timber piles are only going to be used to carry light loads, so why would you need to drill and set one in a rock socket? Driving the pile to rock should be more than adequate.
There isn't enough overburden to establish fixity in the mudline. They want a timber pier for light applications. Small ferry boat tie-up and restaurant over water.
The contractor's said he's done it before. I'm skeptical.
I am skeptical also, but that does not mean it won't work. Ask the contractor for details and look at previous job(s?)
Just because now you have us curious, please post details.
I'll update the forum after we meet in the coming weeks. I've talked to several geotechnical engineers. There all of the same opinion. "never seen it and skeptical".