Is it against any rules? No. Unfortunately, Leveling dungeons have no ilvl restriction. Therefore, you can be woefully undergeared. That being said, if I saw full Shire gear in Castrum Abania, I'd likely kick you. Sorry, but I have no interest essentially being a full time healer since if I even look at DPSing, you'll keel over. Likewise, it's equally tedious for both DPS and the healer since you'll have to do small pulls just to stay alive.