Camo cancellation says: ► The Camouflaged Marker is forced to make a Saving Roll. Para ammo says: ► After a successful attack using Paralysis (PARA) Ammunition, the target must make a PH-6 Roll per impact suffered By my reading, the PH-6 roll is not a saving throw, and therefore being hit by a Riotstopper will not reveal a camo marker, regardless of whether the roll is passed or not.
I'd say it is a saving throw. But the only support for that claim i can find is that riotstoppers in the weaponschart (p.167) have ph-6 listed under "saving attribute."