Check that they have the newest version of Eclipse, which right now is Mars. I had an old version (Juno) so it didn't work. After that, I would review the installation instructions on
the website here with them and make sure they did everything on that list. One good, quick test to see if it works right is to try to make a New Project, and in the menu there should be a drop down for "WPILib Robot Java Development." If you don't get this option, there's a problem.
I hope this helps, good luck to your team!