Do you need to use different pipe dies for plumbing than electrical?

YES! There IS a difference.

Plumbing dies cut a thread tapered from start to finish at the rate of 3/4" in 12 inches, usually 3/4" of thread length on 1/2" or 3/4" pipe.

Conduit uses the same size thread with all the taper in a very short distance at the pipe-end of the thread so that the thread is straight and a lock-nut or coupling may thread all the way onto the pipe without binding and without the use of a wrench.

I've been doing electrical since 1947, and still at it.

The Old Fat Man