Yeah, those gates usually get opened around the time the park is due to close, during the day they are locked closed, although I have seen staff use the keypad to use them for access.
Security is a joke because they have bouncers doing it, not proper security staff, from 5 trips this year I've only been bag searched the once (each time I've been carrying a rucksack), and even then the fat obnoxious cretin subcontractor doing the search not only damaged the bag but also ripped out all my wife's medication and demanded to know what they were for, then threw the bag back at me across the table when he got told to mind his own business, all the while not bothering to search the other half, totally disgraceful behaviour and didn't even do his job properly.
Contrast that to security at Chessington who wouldn't stop apologising when he realised the bag contained medicine and looked like he was going to burst into tears, but still managed to search the bag thoroughly without damaging it or offending anybody.