Yeah, there are parts where you don't need a park pass, but you might as well get one. It's only $10-15 I think. And if you are at Sauveur, may as well go up the Sauveur lift and ski down to Avila- always more fun than walking.
In my opinion Sauveur sucks. Never good conditions and very small hill. It is wide, but the runs are short. I would only buy an Avila lift ticket and stay in the park.