I've had tigers in a number of tanks and a number of grouping sizes. I read and read all of the information pages saying that they are quite aggressive, however this hasn't ever been my experience. Granted, I do get them in a group of at least 6, but I currently have a tank with electric blue acara, the school of tigers, a school of corydoras and a few outliers in the community variety.
The tigers don't bother anyone but each other, which is the whole point of getting the school - they love to bully each other and as long as they have enough targets, no one gets bullied enough to harm them. They eventually establish a pecking order and the rough housing seems to settle down save for occasional spurts.
Introducing new ones to the tank can be tricky, just like the original school, if you ever need to add more, you should get several to give the existing school multiple targets to spread out the bullying. Similar sized fish is also important, since many LFS sell them in as dime-sized all the way up to their 2-3 inch full growth.