and they are responsible for bringing to the captain's attention (if he's the PNF) anything they might run into, on the ground or in the air.
If they are going to run into anything I think the captain will be aware of it. The captain won't have his/her eyes buried in the "temps and pressures" (are we talking piston or jets here ). If the captain is PNF he/she does not rely on the F/O PF to alert them to the possibility of an RTO.