Is it still safer to drive if I find NOS single crimp brake rubbers. I know if I find used surface cracking lines then that will be more unsafe during driving.
It is hard to make a absolute determination on if there would ever be a failure on a NOS set of single crimp brake hoses. If the rubber on the hypothetical hose set is not compromised you might consider how many millions of cars that have been on the road using single crimped (all car lines) brake hoses without a significant number of failures. The point being the odds are in your favor.