Most people will tell you that this should not be a problem, but that was not exactly my experience. DH and I were on the silver plan last December and our plan was to split one wish for lunch on most days. It turned out that our first two lunches were at non Disney-owned restaurants (House of Blues and RFC at AK). The difference is that all Disney-owned restaurants use the same cash register system, which has access to all the wish information, and non Disney-owned restaurants use their own systems.
At HOB our server said that the number of wishes used was determined by the party size - e.g., their system would deduct 2 wishes for a party of 2. According to our server, it was against HOB policy to incorrectly record the party size (no idea why). After talking to her manager, she got permission to list our party size as one so we would only be charged one wish, so everything turned out okay without too much of a hassle.
At RFC our server was confused about what we wanted to do and kept telling us that we weren't getting good value for our wishes. I explained at least 3 times that we were getting a fine value, we were just only using one wish instead of two. We ordered one wish worth of food, and confirmed with her what we wanted to do again before the check came. Since their cash register system is not linked with Disney, their receipts don't show the number of wishes used and the number of wishes remaining like it will in other restaurants. Since I didn't trust our server, as soon as we got back to our resort I went to the front desk to check our total number of wishes. Sure enough, we had been charged 2 wishes by RFC. I explained the situation and showed them the receipt showing only one wish worth of food, and was able to get a credit for the extra wish. Again, everything turned out okay, but it was quite a hassle.
Determined to figure out whether sharing wishes was okay or not, we called Disney Dining to ask. The person we spoke with said that it was up to each restaurant whether they allowed wish sharing. We decided it just wasn't worth the hassle, and didn't share wishes for the remainder of the trip.
So...yes, you can share wishes at many restaurants. However, you should be prepared for a bit of explaining and a bit of a hassle, especially if it's not a Disney-owned restaurant. If you're not sure if you were charged the correct amount, save your receipts and get a wish statement from the front desk at your resort. And make sure you work out with your server whether wish sharing is allowed prior to ordering!
Sorry so long!
