You're thinking Discipline. Tactics is the Vitality/Boon Duration line with healing shouts / banners.
You won't be. Don't worry about taking another profession's role or anything like that; healing is healing, and that's useful for everyone because heals in GW2 are for pretty small amounts.
Tactics is a solid line for dungeon support;
- You revive faster (always good), and gain toughness while reviving (very good, at 80 this works out to 400 toughness; more than if you went 30 points in the Defense line)
- You grant might on revive (not amazing, but useful)
Additionally, a trait like Empowered (increased damage for every boon on you) can be obscenely good since there's usually a ton of boons flying around anyways. Round it out with Lung Capacity (Shouts recharge 20% faster) and Vigorous shouts (shouts heal) and you have a solid support build. You can put points in any of the other trait lines and still be pretty kick ass (I go 25 in arms and run a high crit/bleed build in addition to support).
Worth noting that Tactics line will also be useful for you in WvW: Quick Breathing (Warhorn skills convert conditions to boons and recharge 20% faster) will give you constant swiftness and help thin out conditions on yourself and those around you. There's also two traits in the line related to the Longbow, which is going to be your ranged weapon of choice in WvW for all of the AOE.
There's a LOT of good Warrior builds, and they're all in a really good place. I happen to like the Crit/Bleed/Support spec, but poke around GW2 Database's builds section and see if any sound good.
Edit: Oh yeah, if shouts aren't your thing, you can also roll with a banner build: Inspiring Banners will make them affect a wider area and cool down faster, and Inspiring Battle Standard will cause them to grant regen. It's not as effective as shouts, but it's an option. I've never tried it, but YMMV
