Will an EUS procedure also be able to show if you have a stomach ulcer or gastritis?

Depends. The answer is whether they use a regular endoscope first as part of the procedure for placement of the endoscopic ultrasound scope. Some do, and some don't, so you cannot be guaranteed that all of the stomach and intestines are visualized. If there is a reason that you are concerned about it, you can ask your gastroenterologist how they perform the procedure. Good luck.