No, its a workstation. But it can double as a gaming system if desired (i.e. independent pro that likes to game in their spare time). It won't be the fastest gaming system out there, but it can do it (and has been done by other MR members).The Mac Pro, by definition, is not a gaming computer.
I look at it this way; it's cheaper to get a copy of Windows and a decent card than to get a new system (PC) just to game with.
But it may also be cheaper to get a console, depending on the specific card/s desired combined with the cost of a Windows license (assuming the user is actually willing to consider this route).