Again there are many types of vacuum pumps. Vane pumps can work dry, in oil or in water with electric motors. There are also venturi pumps that work with water or compressed air.
All pumps need some protection from excess resin entering the vacuum lines and into the pump. The danger of this is much larger in the resin infusion process, where a trap collects the excess resin in a bucket. The trap also has a vacuum gauge and plumbing that helps with the setup of the infusion process.