Can a non member swim at the lake for a fee?

Yes

No, TT is not open to the public. You can swim, as a non member, if you are a guest of a member. The member would need to give your name at the ranger station ahead of time. You would then pay a $10 fee to enter.

We just left there last week. There was a sign posted saying that they no longer did day passes. It might pay you to give them a call before you go.