There is no one who regularly posts that I'm aware of who works at NASA. This board was created "sort of" as a result of MSNBC Space BBS (which was supposively cancelled due to "economic considerations"). Many of the posters on this board migrated from the old MSNBC Space BBS.
It should also be noted that it's common on any board for there to be "lurkers" (people that read the posts but do not post) and that people for a variety of reasons do not want their associations known- though a large percentage of reg posters on this board do disclose their associations. Tom doesn't work for NASA but is involved in interests related to space exploration.