Mary, maybe I'm missing something, but why can't your PALS go to the rehearsal dinner with you? I'm sure you could find him a parking spot safely out of traffic flow but still able to see and be seen, just like at a concert, and also he could wheel through the room at some point. There are also lots of ways to stage a dinner besides cheek-to-jowl formal seating. As for dressing up, my husband went plenty of places with his lower half concealed under a blanket, a dress shirt and Propet Cronus slipper shoes his only visible clothing.
You've mentioned that he's using a diaper -- is that because of incontinence?
If he feels awkward about it, there is time to stress-test the concept at another event. I am presuming everyone will be vaxed/masked based on local conditions.
As for using an LPN, CNAs are trained on Hoyers, so I don't know why you would need an LPN just for that. I would certainly not want anyone to learn the Hoyer in a trial by fire -- kind of a safety issue. I would be clear with the agency as to what you really need.
My husband was not social at the best of times, but I know he never regretted showing up wherever he could, all the way through. This is a one-time deal and you don't need speech to connect with others in a room, at a joyous occasion.
Best,
Laurie