DeadEye is correct.
However, I feel we may be wandering up a blind alley here. A blocked breather causing a vacuum in the tank would be likely to starve the bike of fuel when running, not cause starting problems.
It would be good to know what the symptoms are.
You started this thread by asking whether the starter relay could be to blame... is that because it isn't turning the engine over? If so, we're looking for an electrical problem.
If, on the other hand, the engine spins on the starter and doesn't fire we're looking for something else. Reluctance to fire up when hot is often due to too rich a mixture caused by a clogged air filter or the owner employing the choke lever unnecessarily, for example.