I guess my main point is tyres designed for motorsport compared to tyres designed for the street. But whatever, its not worth arguing over.
If you run street tyres on the front and something like R888, Re55, A048 on the rear, it will be very unballanced and understeer like a dog when the rears warm up. I know, I tried it with RE55s on the rear one track day.
However, if by 'semi slicks' he means something like the federals or khumos, he can probably get away with it.