While bullsnakes/gopher snakes can and occasionally do eat rattlesnakes, they are not a main prey source for them. Bullsnakes will not appreciably affect rattlesnake populations in a given area. However, if a rattlesnake has an opportunity to avoid a bullsnake, it will.
As far as snakes being immune to all venom, it is a snake by snake and venom by venom proposition. Some snakes are immune to other snakes venom (kingsnakes and Rattlers) however some snakes are susceptible to the venom of other snakes.
Most snakes are at least partially immune to their own venom, but it does affect them if they are bitten by another snake of the same species or even themselves, but it is unlikely to kill them. If a venomous snake is bitten by another species of venomous snake it may or may not be affected. It depends mostly on how similar the venoms between the two species are.
That said, some species of snake are immune to venoms very different from their own and others are immune to venoms while being nonvenomous themselves.
CM
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