We've seen a couple of alligators in the lake at Coronado Springs. People were feeding them by the lobby. And we have seen a couple in the ponds while riding the buses to and from the parks. Nothing to worry about.
I have seen a snake only once, also at Coronado, in the grass by the edge of the lake. Again nothing to worry about.
We're from south Louisiana and these things are not that unusual. Not in the city but anywhere there is water in the country.
P.S. We have seen turtles, rabbits, raccoons, armadillos, rats and mice (not the Mickey kind) in WDW. Cheers!!!!!!!!!!!!!!!!!!!!!