When playing in co-op both players will receive rewards individually. These are not shared between both players.
During Raiding, Players will receive GenMat based on whether they are able to steal and successfully escape with the material. All loot dropped and experience earned is earned individually.
While Building, Players will both earn rewards/experience during the build, however: Only the host will receive GenMat extracted from the Outpost and will be the only one to receive rewards from Skulls left behind from killed Raiders.