Just be sure you establish it that you're going to be holding adds, alliance wide if necessary. I've seen it way too often that if I don't go in as a healer in spots like World of Darkness, the off tank will just drop like a rock because almost every healer tunnel visions the main tank.
As for the issue of "Too many adds to hold on with people ripping as I go", don't fret. The fact that you're picking up any is still heads and tails above what some tanks do. If necessary, take a few Overpowers to secure hate on the few you have before trying to shuffle over to the next mob. As you run more, you'll get used to where the adds spawn, tend to get clustered, and so on. So that issue will go away with time, tomes, and drops.