Chromis and damsels are related, but not the same thing.
In my experience, chromis are pretty peaceful toward other species of fish, but not as friendly among themselves.
From what I've read, it seems that schooling behavior is most likely when they're sharing a tank with something pretty large, that they consider a threat. My experience, which I've seen repeated in these boards many times, is that a group of six or eight does not school, the dominant chromis pick on the weaker ones, and eventually they whittle themselves down to one or two survivors.
Edit: Interestingly, the article referenced in a previous post suggests the opposite: that large, threatening fish will make chromis more likely to disperse and hide, rather than school.
Don't get me wrong. I like blue-green chromis. I just wouldn't put more than 2 in a tank together.
The idea of cycling a tank with a damsel (or any fish) seems to be a holdover from the old days when people didn't use live rock and live sand. The fish was the source of the bacteria that set up the nitrogen cycle. Now, you can get all the bacteria you need to start the cycle from live rock. Add a cup of sand from an established tank and some plain aragonite sand, and you're set.
Aside from the cruelty to animals aspect, advising anyone to cycle with a damsel is my idea of cruelty to reefkeepers. Once a fish gets into a reef tank, it's harder than you might expect to get it back out. Some people have reported removing every piece of live rock, just to catch one fish. Unfortunately, many damsels are so territorial (nice word for vicious) that removing them is necessary if you're going to keep other fishes in the tank.
Skip the damsel. Don't cycle with a chromis, either. If you don't trust the live rock to produce enough ammonia, add one uncooked coctail shrimp to the tank. Really, for most people, even that's not required.
Live rock comes with lots of critters on and inside it. When the rock goes into a brand-new tank, some of those critters will die and begin producing ammonia. Bacteria from the rock will start eating the ammonia. Days to weeks later, you have a cycled tank.
