You may want to confirm with Disney. If he is coming to your "cake cutting", etc., then he is probably counted as a guest, but I am not sure. Our officiant, Jack Day, did not come to our cake cutting as he had another wedding after ours. Also, I know that there are special rules from bringing an outside officiant so you should probably check on that as well. However, that may be only if they are performing a wedding. A vow renewal may be totally different!
Someone on this board had their uncle (I think) perform their wedding. I believe he had to go to the Courthouse and be sworn in or something to be able to perform a wedding in Florida. I believe it might have been UndertheMistletoe who did this and she doesn't post on this board any longer; however, you may be able to search for her trip report and find the information.