It's all very well listening to Tso like he is the know-all, but it may pay you to take note that the SCCA runs its rallies on a rather different basis to its European counterparts.
Before you go wasting your time chasing about for things he mentions are necessary in the UK, find out what is necessary in the USA.
As somebody that has competed in XC mountain bike racing at an international level, I can tell you that every countries rules are different and every country requires different permits and regulations to be met to compete.