^Well, there's plenty of precedent for one actor playing more than one character in the same continuity. Look at all the characters Vaughn Armstrong played in Star Trek, not to mention Jeffrey Combs, Mark Lenard, Suzie Plakson, Diana Muldaur, etc. Armin Shimerman, Max Grodenchik, Tim Russ, Robert Duncan McNeill, and Ethan Phillips all played other characters on TNG before getting regular or recurring roles in its spinoffs. Patrick McGoohan played four different murderers on Columbo, and Robert Culp and Jack Cassidy played three each (with Culp making a fourth appearance in the revival series as the murderer's father).
Don't forget James Cromwell, who played at least two different characters in TREK before being cast as Zefram Cochrane in FIRST CONTACT.
Heck, he was in a DS9 ep written by Dave Mack and John Ordover.