The actor's voice isn't all that different than the voice he used, all he was doing was imitating the accent... since he and DeForest Kelley's McCoy are the same person... that makes sense...I thought it was pretty lame how he imitated DeForest Kelley's McCoy voice.
Otherwise Chekov there should stop using the same "w"s instead of "v"s thing that Walter Koenig did...