A PPO plan has deductibles and co-insurance, where as an epo plan only has copays like an hmo plan, but allows you the choice of going to who you want to go to, like the ppo plan. If the PPO and EPO are with the same insurance company, and they are a fully insured, insurance comany.. i.e. Blue Cross, Aetna, Cigna, blah blahb lahb and not with a self funded plan or third party administrator plan, then the rules on WLS should be the same for both.
As for choosing EPO vs. PPO, EPO is designed for sick people, just like the HMO plans were, which is why they cost you more in premiums. It will save your out of pocket a lot of money, but the premiums can be quite high. I suggest the EPO plan to people that have illnesses that need lifetime care for. The PPO plans are for people who don't get sick as often, and even the high dollar deductible plans are for people who never utilize healthcare at all. If someone wants to keep their premiums low, they opt for the high deductibles, and their company might offer a health savings plan, almost like a flex plan, to save money for the illnesses that you have. I don't think you get paid out if you don't use the money though, so I wouldn't ever go with a high dollar deductible, especially in your considering bariatric surgery.
Look at the bariatric surgery covered under both plans. Think about how cost effective it would be to have either of those plans. Think about the continued medical treatment you would need after bariatric surgery. That's the only way you're going to pick the right plan for you. Also, most importantly, read everything that plan document says, and if you don't understand it, ask questions. Its better to be safe than sorry with health insurance. And believe you me, they do try to stick it to you illegally too.