They are definitely going to want you to be ulcer-free before surgery---and frankly, if you have ulcers BEFORE, I'd think the gastric bypass/RNY a bad surgical choice. Have you considered the Sleeve or the DS?
The gastric bypass will leave you with a tiny pouch and a huge 'remnant' stomach that can still develop ulcers, but which can't be 'scoped. Neither the Sleeve nor the DS would leave a remnant stomach---just a smaller, but still fully-functional stomach. You REALLY need to give this some thought. We have a poster right now who's looking at a reversal of her gastric bypass due to intractable ulcers---and she's only four months post-op!
Given your BMI, I strongly urge you to look most closely at the DS. It has the very BEST long-term, maintained weight loss, and it's the best at resolving or preventing co-morbs like diabetes and high cholesterol.