Why would you need spacers? Are you shooting 38 Super in STI mags? If so, then maybe but not necessarily. Try them without spacers first and then if you have feeding problems, then go to a spacer. Also, use the steel Hardy spacers for the best results and don't glue them in - per Mr. Hardy. Remember, if you put in spacers, you have to change the follower also.
I thought the normal 9mm was too short in most mag tubes so they needed a spacer at the rear of the mag tube (and matching follower). I'll definitely test it before going to spacers.
I'm guessing a comp designed for 9mm minor would work, so I might look into one of those as well if I don't hear back from the shop that built this open gun.
Thanks for the feedback, everybody! Let me know if there are any other considerations I need to think about.