I confirmed this limitation was added in PRPC 6.3. I also did a little digging and I didn't find any specific problems caused by the hyphens being in the operator name, but the SMEs tightened validation to no longer allow it and that was probably in response to something. Since that was done a couple of years ago, I'd be concerned that newer code specifically hasn't been written with that possibility in mind. You'd need to test your application to know for sure if you'll have any specific problems. It seems other people have replaced the hyphen with an underscore in the operator IDs to avoid the possibility of a problem.
We encountered issues in Pega 6.1 when the operators with hyphen character in the ID are created.
The check should be done during the save of the operator to safeguard against problems.
You can save the data by running an activity to create the Data-Admin-Operator-ID record, but you may run into other issues down the line (I have previously seen problems with Bulk Processing when using operators names that contain hyphens).
FDBK-5918 had been raised to request for support the use of hyphen in the Operator ID.