The rest of the story goes for a light twin prop, where a big part of the lift is generated by the propwash. If you would have flaps set for t/o, and you would have an engine failure, this would mean that the wing with the working engine and the flaps down, would give you more lift than without the flaps. Therefore the speed to maintain direction would theoretically be higher with flaps than without, therefore the flaps in t/o position requirement
As I just explained, it all depends on type of flaps+prop location in relation to flaps. For a Piper Aztec with floats for example Vmc is 14 kts LOWER with full flaps than with 0 flaps. On the Reims Cessna F406 it is 10 kts lower.
Zakka