What special airspace exemptions are granted for civilian fighter jets?
The same regulations apply to civilian ex-military aircraft as they apply to any other aircraft. Whether flying IFR or VFR, you will need to comply with the same rules, e.g. speed restrictions, airspace restrictions when under VFR, meteorological conditions, etc.

An exception can be speed restrictions, where a speed restriction would be in contradiction with the parameters of the aircraft to perform safe flight, e.g. the minimum clean speed being above 250kts or similar.