No. Simple as that.
Although technically it would deal damage as if Multiscale wasn't there, since Multiscale halves the damage done at full health, which a crit would double the amount of damage done.
For example, if a Dragonite (a common user of Multiscale) had Multiscale and was at full health, it's Ability would cause the damage dealt by any move to be halved. However, a critical hit would neutralise that, since critical hits cause the damage dealt to be doubled.
