Hello and welcome to MedHelp forums. We can't advise anything that is contradictory to six doctor's opinions. In general, whey is a protein that comes from cow's milk. Manufactured whey will have the same impact and unfortunately, isn't suitable for all based on digestive issues. With whey protein, there can be an increased incidence of diarrhea. As ulcerative colitis also has issues with diarrhea, you can probably see how that would possibly impact you negatively. Has it been suggested that you limit dairy products because of your GI diagnosis? That's a pretty common recommendation.
Here's some dietary information regarding ulcerative colitis to stay healthy. https://www.webmd.com/ibd-crohns-disease/ulcerative-colitis/vitamins-and-supplements-for-ulcerative-colitis#1
Now, this is your life and your body. You could try small samples of whey protein and see how your body reacts. But in general, it's not well tolerated by those with your condition.