I'm currently maining a Hunter. He is 4/7 in Firelands and pretty high dps. Thing is, though, I mained a Druid all through BC and Wrath, and I'm really starting to miss it. I was and still am Feral DPS. My question is, if all I'm really wanting to do is DPS and PvP along with some old content here and there, would I be best off just staying a Hunter? And if I do decide to go with my Druid, what reasons can I give my raid leader that might persuade him to let me bring my Druid in my Hunter's place? (We do not have a Feral in our group)

choose hunter for yourself!

If there is another hunter in the group, I think you should go with the druid. It sounds as if you had more fun playing the druid, and Ferals are pretty good in raids. To tell your guild leader, just straight up say you want to be a druid. If you're a good raider and have good druid gear, or intents on getting some, I doubt he will mind.

Hunter - Amazing for pvp at low levels, not as good at 85. However, they do fairly well in PvE and raids. (survival hunter's have ridiculous dps).

Druid - Good for pvp at 85 and also decent in pve (their bleeds are amazing). In my opinion this class is also more fun and there is more variety since you can play healer, caster (like a mage), and a feral (like a rogue).

If I were you I would use the druid.