Real rallycross tyres are slick-like tyres, depending on event they aren't cut at all (no tread pattern). The FXR handles very nice on rallycross tracks with current slick tyres and proper setup. Hybrid and knobbly tyres are more like rally tyres. I guess their existence is due to the simplistic (or the lack of) gravel physics.
And, like said already, the FXR as a GT racer doesn't really resemble rallycross cars. What I'd like more (and what I've suggested quite a few times) is that the devs would make proper Div1 (& 1A, 2 etc) vehicles. And some better rallycross tracks.