Which version of Genesis? Anything below 3 is not worth the effort.
OK the Mixamo animations is 100% compatible with MotionBuilder so you could import the animations into MB and attach a control rig and re-target the animation to the Genesis 3 model.
101 stuff though if you want to retarget using MotionBuilder the first step is to add a control rig that you can plot the base animation to a set reference rig that MB understands.