I need to replace the hot water supply valve under the kitchen sink. I cannot find the whole house water turn off. If I turn off the hot water tank supply valve, will that suffice?

If all you're working on is the hot water the answer's yes you can.
If the angle stop's what you're replacing a compression angle stop then simply reuse the old compression nut and feral and attach the new stop to it. This will save you time and hassle. Good luck, Tom