I have a hardware device that has a WiFi chip that requires port fowarding on a router to normally work. That is, my server sends data to the router, which has port foward info to foward data to my Hardware's local IP.
Now, I need to do the same thing with a iOS WiFi hotspot. I know you can't do it off the bat, however, I believe you can hook up the iOS to a Mac via USB or WiFi, and somehow make the Mac perform the NAT to a local IP. Perhaps, even make the Mac broadcast your iOS Internet as WiFi, and do the port fowarding from there.
I have seen this done on Windows. http://www.youtube.com/watch?v=Vda8NySEy04 However, I have no idea how to do it on a Mac.