It is possible for an outboard to run with slightly damaged reed valves, but it will generally be hard to start. The other main symptom of bad reed valves that are either broken or not closing properly is seeing fuel spit out the front of the carburettor. This is because the fuel mixture in the crankcase is lightly compressed as the piston comes down to push it into the cyinder through a transfer port. If the reed valves don't seal properly this won't happen and the fuel-air mixture will be pushed back out the same way it came in - through the carburettor.