As long as you can get the disc to the ground at the right angle, it doesn't matter what you use. But an overstable disc will be more predictable and roll straight for longer, FH or BH doesn't matter.
For learning the shot though, generally you want a stable to understable disc for backhand rollers, and a stable to overstable disc for forehand. It's just easier to get the steep release angle and torque on a FH roller to get an OS disc on the ground and rolling straight than it is with a backhand.
I can get the same distance out of either, but I FH roll with a XXX thrown on a steep anny, and BH roll with a Vision thrown with just a slight anny. FH is definitely more consistent because I can get it to the ground quicker and the disc fights against flipping over for longer. If I could get the same torque and release angle with BH then I'd gladly roll a more OS disc.
