If someone is in an AoE (let's say a fireball) that grants a reflex save and he is riding a mount. Does the mount get a seperate reflex save? Or does he the player make ride check (because his character is trying to steer the mount away). Or is the mount considered part of the primary reflex save the player makes?
all three these options seem logical to me.
I think both the mount and rider make a check. I think their is a feat that if your horse fails you can attempt a ride check, but that may just be for regular attacks. I'll check.
Indomitable Mount (Combat, Local)
Once per round you can substitute your Ride check for your mounts saving throw.
Prerequisitites: Mounted Combat, Handle Animal 5 ranks, Ride 5 ranks, Lastwall affinity.
Benefit: Once per round when your mount must make a saving throw, you can make a Ride check as an immediate action. Your mount makes its save if your Ride check result is greater than the DC of the opponent's attack.
Source: Cities of Golarion
Mounted Combat (Combat)
Avoid attacks on mount with Ride check
Prerequisitites: Ride 1 rank
Benefit: Once per round when your mount is hit in combat, you may attempt a Ride check (as an immediate action) to negate the hit. The hit is negated if your Ride check result is greater than the opponent's attack roll.
Source: Pathfinder Core Rulebook