It's copyrightable if it runs Drake's voice through software and then generates an imitation. It's not if he personally listened to a lot of Drake and recorded his own vocal imitation with off the shelf instruments.

This is a PR stunt, it will never go to court anyway. But if it did, the way to have done this legally would have been the Death Row Records approach when Snoop Dogg left them in 1996. They simply signed a rapper who sounded like Snoop, gave called him Top Dogg, and had him perform guest verses for other label acts. He appears on 2pac's "All About U", recorded at a time when both Dr. Dre and Snoop had left the label.