You can play whatever "role" you like, yes - if you have bought the action you can use it, and buying a certain action will never lock out another action. I'm a master healer, decent nuker (DPS magic), and semi-useful Offensive Magician (Title says it all. Well, ok, really OA is debuffs. But I like "Offensive Magician" better). And I can use any, or all, or none of those "roles" in the same day - in the same kill, even. :)
