The 'motor generator' part of the device must have a voltage of some kind coming from it. If that voltage can be converted to something a standard inverter can use then there is no reason why you can't do the substitution as you suggest.
Do you know what the motor-generator side actually puts out? I suspect it won't be anything 'normal'.
It appears to be 3ph, no idea what the voltage is, have to check that tonight.