i had PT LE installed on a mini with sl server for about 3 months, and never had any issues. i mostly used the computer for editing, but had LE, various plugins, etc all installed and ran fine.
i think server really just has some additional functionality, but doesn't really hamper the way the client services programs would run. fyi, you won't have garageband or iLife if you buy that OS. one other thing i discovered is that you can't share external hard disks that are connected to the mini with sl server (or at least not as easily with client sl). like, for instance, i had an external drive connected to my mini that i had time machine for my macbook to back up too; couldn't figure out a way to make it work like the easy way it is to do with normal sl.
also fyi, you can run the client version of sl on mac mini's if that's the direction you're going.
hope that helps