GateKeeper will definitely sap up queue wait from other roller coasters in the park. Recent changes to the Fast Pass however will add an underlying factor for 2013 that will change queue times.
The Fast Pass will now be a two-tier system - the basic Fast Pass will grant entrance to all previously listed rides, EXCEPT TTD and GateKeeper. For those two roller coasters, you will need to pay extra.
TTD had plenty of issues with Fast Pass last year; essentially operating on one train operation for Fast Pass, one train operation for regular. I'm glad Cedar Point is taking action to fix the TTD queue, but this inevitably means that there will be more regular Fast Pass users for other rides. The ride base has been reduced (number of rides), and statistical chance of having more Fast Pass users per ride will increase. And let us not forget - regular Fast Pass users will still have to wait in the regular lines for GateKeeper and TTD, lengthening those lines.
So yes, GateKeeper's queue will absorb riders from other coasters. However, Fast Pass usage has been restricted, meaning more Fast Pass users will be waiting for Maverick, MF, Raptor, etc. It could very well be possible that queue wait times stay relatively static, and do not change as a result.