Yes, I went through a similar thing recently; horrible bleeding diverticuli for a week. I didn't have steroids, though -- brought my own T1D, and own insulin.
Are they giving him a saline drip, too? It might have dextrose in it. If they are giving antibiotics intravenously, ie. Cipro, that may also have glucose in it.
It depends on which hospital you end up at, whether they consider diabetes/high glucose a significant factor. The one I got stuck at for a week, said their protocol was "sliding scale" insulin of their specific choice, and only after a person was over 180 mg/dL. (That's 200% of normal, and feels horrible to me, personally.)
The hospital's idea of a "diabetic food menu" was to put a sugar-free iced tea on the tray instead of regular. I was at a different hospital before, and they very specifically "asterisked" low-carb "diabetes menu" items. I wasn't allowed to order anything else. Haha. Fine by me.
Technically, you don't have to eat what they serve. You can ask for alternatives, or bring your own food. Usually, the menu is customizable. And the kitchen and nurses got easier to work with once I figured out the menu system, and who to I needed to talk to. If you aren't "eating," then they want you on a stream of glucose for energy.
At first, they gave me juice and sugary soda and high carb foods. And the cafeteria worker would just come in an hour later and roll their eyes, and throw the whole thing all away because I wouldn't touch it. I had to ask for different, and be very specific, or at least choose only the non-high glucose options. They had a kind of protein jello ("gelatein") when I was there, and one flavor had less carbs (2g) vs. the other flavors (20g). Had to read the label. My glucose was all over the place till I figured out all that they were doing to me with the drips and the food. You want sugar-free, ask for sugar-free. You are in charge.
Hopefully, your dad will heal up and be able to eat solid food soon, and then get out of there. And the steroids will quit with the elevated glucose. If he needs a shot of insulin, it will probably be all right. I don't prefer to be high at all, ever. Healthcare workers tend to stick to uniform instructions and doctor's orders, unless they are told to stop. I had to demand they quit with the sugar drips; and they kept saying I needed it. Well, they switched to saline-only, and I didn't die when they stopped, and felt better.
But that's just me, and my situation. I didn't have a intestinal operation yet, but almost everyone in my family has, and almost everyone in my partner's family has, too. Diverticulitis is a nasty beast.