I only have the one account on the live servers, and it works like everyone else's (barring name color). No special permissions, access, or anything like that. Since I like to be able to try out a variety of decks, I draft a lot and build elaborate spreadsheets to track getting to rare complete. I play a good bit, and it's also pretty easy to convince myself to spend on the game :)
Most real testing happens on our internal development servers. There everyone on the team has many accounts with 1000 WCs, etc. so they can test whatever they need to, try particular decks, whatever. For example, before each emblem event we'll have playtest rounds on these internal servers to help us test what does/doesn't need to be in the ban lists. But for understanding what the real metas feel like, there's no substitute for playing on live.