It was an option, so maybe. Does his truck have a key FOB for it now? If so, does it look like a Ford factory one, or different? If there is an after market keyless entry system, look under the dash for the control box and then google it to see if you can find the instructions to enter the programming mode.

If the truck never had a key FOB, then odds are, there is no factory GEM. You can still have an aftermarket keyless entry added though.