See what all the other SAR folk in the team are using.

My SAR team, we have a wide array of packs from Gregory to Osprey to Mountainsmith, to specialized packs that cost a bunch, to former/current Army/Marines who just use their military ruck. I would have him keep using the Granite Gear for now. My pack is a 40 liter Gregory.

What he needs is to keep going to trainings and to start accumulating the recommended gear - do not buy anything extra until he has the gear list in hand to inform your purchase. SAR gear can be very similar to backpacking gear, but there are additional items he will need to carry in addition to the tent/sleeping bag and he will also be going to trainings that will increase the gear needs as he goes along if there is a need for water and alpine rescue in the area....

I would start by getting his measurements at an outfitter, so you know what back/hip belt sizing he needs. Then look at 30-50 liter packs without a lot of mesh and loops on the outside of it. In terms of gear, think in terms of less bulk and less weight - the lightest stuff he can get for the "backpacking and camping" part of it will help him in carrying the mission related junk like ropes, helmet, climbing aids, ice axe....

Also have him ask about pro deals - paraprofessionals like SAR volunteers can get some sweeeeeeeet deals.