Ofiomante

If the ability does trigger, but you control a Snake when it tries to resolve, the ability will do nothing. No Snake token will be created.

Ophiomancer's ability checks if you control a Snake at the beginning of each upkeep. If you do, the ability won't trigger.

Ophiomancer's ability considers any creature you control with the creature type Snake, not just the tokens Ophiomancer creates.