NHTSA doesn't have a hand in the OBDII world, that is the EPA's cup of tea. RB's will pass emissions with alittle bit of care, the issue isn't that it's not possible to do OBDII on a R33, it's that no one has a system up and running for the compliance process.
Now if a RI has access to a system and can get a ICI to install it then all is well, but again, it's not that it can't be done it's that no one has one yet. However, JK Tech claims they are able to do this and I'm sure if that is accurate that they obtained the rights and privacy to the designs so no other RI could use it, just as they did with the air bag system that's required for the complaince process as per the Addendum A.