I concur with Michael. Depending on the type of tent you have (and how you like to use it) you could put the tent on the actual pad and not stake it down (if you have a tent that the stakes are only to hold the tent from blowing away, as opposed to holding up the poles and tent itself). Of course if they are the kind of folks who like to sleep on the ground (no cot, no air mattress, etc..) and just use maybe a sleeping bad and sleeping bag, it could be quite "Firm". I think that most people that bring tents to the Fort are probably bringing a cot or an air mattress to sleep on, so it's kind of nice having a firmer foundation to put those things on (The concrete under the tent).
You might get away with putting the tent behind or even to the side of the site depending on the location of the site and the size of the tent, but be aware that it does seem that they are starting to be stricter about the rules. One of which basically defines your site. (Typically it's words like "Half way between your site and the neighbor site).
My advice is that if they are not willing to put the tent on the paved area, then you should look for a separate site. If you they are willing to put it on the paved area and your assigned site has space (without violating the rules) to put the tent, then you got lucky.
A huge factor in all of this also is, "What size is the tent and your TT?"
