Depends on the system they use, they often use a few. If you get there early and queue in the Annual Pass queue (on the right hand side of admissions) then somebody usually walks down the queue scanning passes and stamping hands. Then you just walk through the gate showing your stamped hand. If they're not doing this then there is a scanning annual pass turnstile, where you just scan your pass to get in, along with a manned gate where the person checks your pass and you walk through.
Annual Pass holders are also allowed into the park 30 mins before rides open for early ride time.
Hope this helps!