By the game's own definition, when you enter a raid, you are a raider.
If you clear old raids for trasmog gear, you are a solo raider. If you get a group together for previous expansion achievements, you are an old school raider. If your guild takes a shot at MV once a week, you are a casual raider. If you are competing for realm firsts, you are a hardcore raider.
We don't say that DS isn't a raid anymore, so why would we say the people doing them aren't raiders?