We used a honeymoon registry and it worked out really well! We filled it with high-end things like plane tickets, park tickets, hotel nights and rental fees, and lots of little fun things like Mickey bars, a round of mini-golf, Butterbeer at Universal, drinks at Epcot, Ice cream at Ghiradelli, etc. People seemed to react well to it, and even though we also had a traditional registry, we received over half of our honeyfund items.
Some sites charge, but I used
https://www.honeyfund.com/ and it was free. Beware though, I spent a ton of time making cute avatars for all the items on the registry, only to find out that they would only be seen if I paid $50 for the special edition.
As long as you don't include any registry information with your invitation (which is poor etiquette, and essentially asking for a gift), I can't see anyone finding it tacky. Just explain on your website that you have everything you'd need and that if someone were considering buying you a gift, you'd love for your honeymoon to be really special.
One last tip- buy and wear the bride/groom ears. We were given them as a gift when we got engaged, and though we thought they were a little cheesy, we decided to wear them the first day that we were there, and then ended up wearing them for the whole trip. We got so many extra little perks- instant fast-passes, a free ice cream bar, moved to the front/center for Holiday Processional, etc. Have a great time!