No it won't, not without tweaking- it has a low voltage sensor designed to blow the ballast when the battery drops too low. I expect it's little more than a voltage divider (two resistors) feeding into the microcontrollers A/D input, so it could be easily modified to accept a lower voltage, if you're happy with that kind of work.
You sure the original motor does 8000RPM? Sounds a bit low- what's the gearing on that drive , 2 or 3:1? The Graupner 500E does about 12000RPM at 12 volts, and should be fine driving the seawolf with a bit of gear reduction. 308 hobbies still had some Protech mega-X 500 motors in stock last time I dropped by, which is the same motor but about half the price the Graupner model.