[usbcd36]

There are no rules specifically governing encoders. As long as they comply with all of the other rules, (safety of materials, etc…) they are fine.

Don't see why you aren't using the KOP encoders, though. In case you're wondering, they are 250 CPR optical quadrature encoders, part E4P-250-250-D-D-D-B. The datasheet can be found online from the part number.