You cannot safely run E85 with a supercharger on a new GM flex fuel vehicle. This is due to the method in which GM calculates/estimates ethanol content. Since 2006, there has not been an alcohol sensor in the vehicle, instead the ECM relies on a calculated approach that compares pre-fill readings to post-fill readings. That calculation requires the engine to be run in closed loop for the first 10-15 miles after fill up (with few exceptions), which is dangerous for a vehicle which needs significantly more fuel when in boost.
The fuel injectors are too small for boost and E85 and the fuel pump is going to be tasked at high RPM as well.
If you install an alcohol sensor to discreetly determine ethanol content, then there won't be any problems. We have one sitting on the shelf waiting to go in my Denali along with Injector Dynamics ID1000s.