You're right about the cooler, more stable air north of the front not supporting tornadoes, but convective cells in the immediate vicinity of the frontal zone may have an enhanced risk or tornados, due to the increased low-level shear near the boundary, which may act more like a warm front or stationary front as the storm approaches. Anywhere from the frontal location and southward will have the greatest tornado risk. As SPC points out in their Day 2 outlook, the risk of tornadoes will increase sooner than it normally would with an approaching hurricane, thanks to the large wind field and increasing flow aloft, and may commence as early as tomorrow afternoon or evening.