If I have a spa panel going to a simple still dragon controller (manual control) I am only using two hots and a ground, no neutral in my controller at all.
Does the GFCI still work?
Yes. In your case the spa panel will monitor the current on both hot legs to make sure they are equal. If it detect an imbalance it will trip the breaker. An imbalance would indicate current flow to ground.
Yea, that's what I thought. Just started wondering when I did not have a neutral to hook up.