I don't know what to say. Can he eat and function with the cleft alright? If he is able to, I personally would opt not to do further surgery. There are dogs out there that live good lives without surgery. My boss (a dentist) is on the cleft palate board and yes, they are human, but sometimes partial corrections are the best options.
My Abby was diagnosed with a torn knee ligament and during x-rays they also noticed hip-dysplasia. They recommended surgery. That is when I looked into herbal supplements to help her. To date she is older and slower, but she has lived a good life and did not have surgery. Orijen has been rated the top dog food around. I use it personally. If you vet recommended the different food, please be aware, they do not have nutrition education. They will listen to the rep and order based strictly on the trust of that salesperson.
You are going to be the best to know what is best for Buster. I hope that is becomes easier for you as you listen to other members stories.