I too am coming to this thread late: please forgive me I didn't read all the replies so far but I just had to add my two cents, which with inflation is worth about a tenth of a cent LOL
You said:
"However, I'm very aware that we are still non-traditional in that we're a gay couple. And I can assure you that I am also aware that to a large population, we're not welcome."

That just about broke my heart, Rick! Bless you and your partner for being in such a loving, long term relationship! Love and family are what matter, life is too short to worry about other people, do what your heart tells you. I do totally admire you and your partner's desire to be discreet (I'm hetero but I'm not into PDA's either!) esp. not in a place as kid-conscious as WDW. You are surely two very classy gentlemen!
You deserve to have a wonderful anniversary, and I wish we could see the joy on his face when you surprise him! Wherever, or however you do it, it'll be beautiful.
We just stayed at the Grand Floridian about 2 weeks ago and I was just thinking...what if you gave him the ring on the beach? While the fireworks were going off? After a glorious dinner at V and A's (Or Narcoosees, which had FABULOUS food and a great view!) You could give it to him on the veranda outside Narcoosees if you wanted...there are so many great romantic spots hidden in WDW for such a thing!
I'll keep my brain percolating if you still need ideas...and again, congratulations on your anniversary.
Do not even worry a bit about the hotel staff, Disney cast members are instructed to be very sensitive to every family no matter what the situation, and there are many, many CM's who happen to be gay too so I'm sure that they will do all they can to make your stay a joy. I hope they surprise you with something really special.
Where are you staying? Can't wait to read the trip report!
Hugs to you and pixie dust for a great trip!!!