Whist's i agree completely that dual regulators would be a complete waste of time and money, functionality wise i cant think of a reason it wouldn't work? especially on a N/A system where the fuel pressure would not vary as it would on a turbo'd system.

Shame I cant find any leak-off spec for that aeromotive FPR.

Honestly OP, at 550bhp a standard Bosch FPR will more than likely be fine, if you want complete security a fuel pressure sensor(transducer) will be another tool to your arsenal in making sure the engine is running well. I'm not sure how you can calculate the leak off without physical testing of pretty much every component in the fuel system and have the engine running to know how much fuel its consuming across the whole map.