From the hotel what will I need to do for transportation to get to the airport for a 6:30 am flight?
I agree with JohnnyHan. Taking the vaporetto to the train station and then the bus to the airport would take a long time, if they even run at 3:30 or 4:30 am. Take a water taxi. It's pricey but exhilarating.
Before we arrived in Venice, we already arranged for a water taxi to pick us up on our departure day. He was right on time at 730am. I'm sure they could accommodate your departure time.
Get an answer from Hotel Campiello staff and past guests.