I'm no expert on spins and their aerodynamics, and happy to be corrected on this one (Genghis?). But I believe recovery from a spin in a twin would be difficult whatever method you use, because of the inertia in roll due to the mass of the engines not being on the roll axis like it would be in a single engine aircraft.
As to whether asymmetric power would help you recover.... I'd much rather just keep well clear of the spin altogether in any aircraft not certified for it, but especially in a twin.
Back on the subject of the effect of the gear, and the idea that it moves the C of G rearwards.... on the Beech Duchess, the main wheels retract inwards and won't affect the C of G at all. The nose wheel retracts forwards, so the C of G will be further forward when retracted, not further back. But whichever way the gear retracts, I still maintain that any effect on Vmc would be tiny, and it would be type specific whether Vmc increases or decreases because there are several factors at play which all counteract each other.
FFF
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