Back to the topic at hand, pro day is friday, in the last few that I've been at it's been the only pro day in the whole state so you get UM and MSU kids as well as one or two guys from a few of the in-state NAIA schools.
As for who will be working out at it? There should be a bunch I'd bet. In the last few years guys that you wouldn't even think of would be working out in it as well. We as fans have our opinion of who "should" work out at pro day as those that we think is most deserving of getting a shot, however most all of the seniors on the teams think they deserve a shot.
So that said, those I expect (or know/have been told) that are working out on pro day are Sambrano, Moutra, Middleton, Burton, Opperud, Sabin, Middleton, Waldhauser, Alt, McSurdy, Shaw, Roots, Tru, Lisowski, McCord, and McKnight at probably the very least. I believe Fether is teaching in Helena (as someone posted on egriz), I'm not sure if Duncan is in town anymore, same for Lapan I know he's student teaching.
I know that some fans would jump on this and say this is just me claiming that every player is just one good 40 time away from the NFL or something - but I don't think that. What I'm saying is that expect a large majority of our senior class that is here in town to be trying out at pro day, and while only a few will get invites - these guys will give their best to try to show that they have the talent to at least get a training camp invite.