Rocksteady and Bebop appear as extras in the 80's cartoon universe. The Turtles only traveled through space to get to that dimension, not time, as evidenced by they and April being used to the routine of rescuing her.
It's a bit odd that while the 80's Shredder finds the Utrom Shredder off-world simply by doing a scan, Krang is not found at all, even though an Utrom named Krang had a rather brief cameo during the run of the 2003 series.