If you have Red Hat Enterprise Linux, why don't you just call or e-mail their support line? If you want to know to inform your purchase decision, you could also give them a call and they'll be able to inform you.
Before calling, be aware that they'll ask you what these users will be doing. Are they terminal-only users, are they going to run a full graphical desktop, or are you only asking about file sharing? If they are going to run a full graphical desktop, what kinds of programs will they use? How big and beefy is your server?