Strictly from a threat generating standpoint, Seal of Blood would work better than Righteousness, even with a 1 hander. And true, you'd need healing and that would keep your mana up. If you're new to an encounter, I definitly wouldn't suggest this though. Imagine your first Prince fight, trying this out (applies to DPS as well) only to get @#$%pwned by enfeeble.
Using Seal of Blood for tank threat generation is something I'd classify in the "Hot Dogging the Raid" category... You know, things like having your OOM-kin tank Ragnaros... etc. But it certainly has a place.
As for Moroes... between Wings, Judgement of the Crusader (Didn't see that one in there), Avenger's Shield, Holy Wrath, Exorcism, Consecration, Holy Shield and White Damage.... You should be able to build a comfortable #1 threat lead. Gear up a bit and swap to main for some encounters and you'll feel the difference. Or just get beat on by an add at the same time.
Wings, Crusader, and Holy Wrath seem to be neglected quite a bit. Wings and Crusader together = some of the biggest TPS numbers you'll see. Holy Wrath does more damage on 1 target than Avenger's Shield, and has a 19% spell damage modifier, where Holy Shield has a 14% modifier. Not only that, but Avenger's Shield should slow the mob (or even a group of 3) down enough to give time to let off a Holy Wrath... just a thought. With Exorcism, you shouldn't need to judge Righteousness immediatly, especially with the extra threat from Crusader.
As long as you get hit to regen some of that mana, you have the abilities to frontload STUPID ammounts of threat on undead/demons. Well geared DPS should always be *able* to overtake you in end-game (where they had no chance to come even close to you while levelling) but they should be able to open up with some very nasty combos with the kind of threat you can put out.