That's the first order idea, sure.
But if all Vmcg involved was a yawing moment due to an engine asymmetry and a countering yawing moment from the rudder, the manoeuvre would track straight down centreline, with the nose first yawing one way then the other, but no deviation. This, of course, is not the case.
What makes the aircraft deviate - primarily, it's the sideforce generated by the yawed tyres. Vmcg on an infinitely slippery runway would have a much smaller deviation, but it'd also be much harder to stop the deviation once it was happening. Traditionally it's assumed that the reduced sideforce capability of the gear cancels out as the runway becomes more slippery.
To be honest, while there may be an effect, it would be swamped by any kind of crosswind effect, which is a definite real world factor and also ignored.