The CCCP (essentially Russia plus Ukraine) used to put 20 mm aircraft guns in their Salyut and Mir space stations. So there has been weapons in space for a long time.
An EMP nuke in space is not very useful, since it would destroy your own equipment also. It reminds of the so called Backyard Bomb that can destroy the whole planet - probably only deemed useful by a crazy Iranian mullah.
Small targeted EMP/microwave devices are useful and used against drone swarms for example.