Yep. All you need is BLU/NIN and BLM/BRD to proc all spells provided it's not Lightningsday, Lightsday, or Darksday. Bring a tank (THF or NIN) and you're good to go. BLU can cure the tank or if the tank subs DNC, can usually cure themselves. I've duoed a lot of seals for people as BLM and them as a tank, and it usually went okay. Took hours, but was okay.

If you want fast kills, I'd suggest a THF, BLU/NIN, BLM/BRD, and WHM/RDM. Find yellow, proc it, and zerg it down.

Edit: Just realized, it'd be nice if there was a way to lock onto seals that the party is after. Some sort of item that persuades the monster to have an affinity towards one job. Not that it'll always drop that seal, but that that seal is more likely to fall would be awesome. A lot of times my groups just want one kind of seal and it's usually the one seal that doesn't drop.