Can pneumonia/flu shot temporarily raise blood glucose in a diabetic?

Not much: Any stress can increase blood glucose some, especially in diabetics, and a vaccine is a minor stressor on the body. That said, the effect is small enough to not be of clinical significance, and the flu and pneumonia shots are VERY important for diabetics, because the diabetes compromises the immune system. Try to avoid snacks, desserts, rice, potatoes and bread if your sugars are running high.