No reason to wait, just put the application in today. It doesnt cost anything and you don't need to write anything, just fill in your details. Better to know sooner than later so you have more time to figure something else out if it doesn't workout.
Apply through the official site, it's online and 1 page long. No reasons to wait, it takes 4-6 weeks for the application to be approved and it valid for 1 year.
There's absolutely no reason a legitimately issued volunteer visa would be a disqualifier for the elite visa. There's plenty of NGO's and even government offices (translator's in the police offices in Bangkok?). That agency just doesn't want to deal with it.
It's Garrett, not Garreth. And there's no such thing as an "Elite visa agency." There is 1 government owned company that manages the Elite Visas. Some visa agencies can submit the application for you and collect a referral fee if you end up buying it, but that's it. Whatever agency's you talked to probably wanted to sell you something more profitable to them.
ONE person reported not being able to be issued the elite visa after being on a vollenteer visa. ONE person, and there could have been other issues he didn't tell us.
When you submit an application, immigration does a background check and approves or denies the elite visa application. Only way to know is apply. It's free to apply and the acceptance letter is valid for 1 year so no reasons not to apply and see what happens.