Theymos and Badbear can, but probably won't read your PM's. There will be exceptions though, I think once the Feds asked theymos to hand over someone's PM's after they discovered he had been part of/running (can't remember which) silk road.
I don't think he turned over the PM's in that instance, just the posts that were deleted on the "heroin store" thread. The original subpoena didn't say anything about PM's IIRC.
The post that implicates altoid in the SR was deleted, and theymos said there was no backup of it as it was a long time ago. I don't think anything theymos handed over was ever used in the case, I only saw screenshots of the thread and screenshots of the Google search that led them to it.
You are correct the
subpoena only asked for posts of altoid (as well as the herion store thread).
It is interesting they asked for things that were publicly available, especially considering that for much of when the thread was being discussed the forum was not keeping records of deleted posts, so mostly speaking what the public could see is what they got