There's an important differentiation to make. Just because you don't have a power doesn't mean you don't have the thing attached to the power.
Best example: Say I'm a were-pidgeon. But I don't have enough refresh to buy the "diminutive size" power. That would mean that, when I transform, I'll be a 6 feet tall pidgeon. That certainly has potential, but isn't usually what you're going for.
Powers in Fate give you bonuses for something, they don't give you the baseline "you have this" as it might be in other games. So with or without the power, you're still the size of a regular pidgeon. But with the power, you have learned to utilize your size to the effect the power describes.
So just by being a red court infected, which is represented in your high concept, you would have fangs. Not because of a power, but because red court vampires have fangs. Without the power, you just aren't very good at weaponizing them, which is why you don't get the bonus to stress when attacking. Once you have the power, you get that bonus.
The discipline roll is only done when using the powers attached to the hunger. If the scene is dangerous enough, he'll probably have to use quite a bit of his powers, which will eventually mean he will need to feed. He'll probably have a high discipline skill as well, so he won't take too much stress even then. That's ok though, infectees without discipline don't stay infectees for long.
But rolls don't have to be the only way the hunger acts. You can very much compel his high concept in order to make him deal with his hunger.