I can’t answer for certain, since I don’t recommend slaving drives on my DRIVER board.
However, I would imagine the motors don’t really care if they are slaved. However, the driving electronics would need to be prepared to drive double-the-current and double the inductive load. Can you share what it is you are attempting to accomplish?
By “slaved” do you mean using 2 motors on the same (mechanical) axis but driven by separate channels off the board? Check your control software for that capability — the 2 separate channels would have to get the same control signals and the motors should then act identically (for identical motors). That should be doable.
If you mean driving 2 motors off the same channel in parallel off the board, that might be a little iffy.