If the CM is getting you in on their Main Gate pass, then yes, they have to be present as mentioned above.
But if they're giving you some of the comp tickets that they're given a few times a year, which are either a plastic ticket or more common lately a voucher in a pdf file they print out or email you, then no they don't have to be there to use it. The voucher can be linked to your MDE profile ahead of time to make FP+ choices, and if you have a MagicBand on your account already you can use it to access the comp ticket. No need to stop at Guest Relations to exchange the voucher.
We used a couple of these last June. A CM friend gave us 1-day tickets, and then we had 2-day tickets from a convention group we were with. Was able to link it to MDE with no problem. We did stop at Guest Relations to double-check we didn't have to exchange anything, but more importantly to make sure the CM comp ticket was listed on our accounts first above the 2-day since the CM ticket was a park-hopper and that first day was the only day we needed to park-hop.
-Rob