HOT TUB - gut check 1

I'd be more concerned about the eccentric load on the beam if there is any.

Use HDG or Stainless. Don't mix them. Zinc and Stainless are very reactive and galvanic corrosion will eat those nails.

I remember watching some webinar recently discussing what it would take to completely protect the deck members and fasteners from this type of corrosion. The consensus was a veritable jungle of flashing details that would be completely impractical. Even if you use zinc-magnesium hangers or stainless steel hangers, what about the beam? What about when the wood rots out, first? A design like this doesn’t warrant a corrosion consultant. Follow AWC’s deck guide and don’t mix metals. Good luck!

Don’t mix metals.

Use both HDG fasteners and nails. Then sleep like a baby.

I'd be more likely to specify galvanized flashing cap over the nailer or more like specify the hanger to be welded on the beam before being HDG.

You are overthinking this.