I always wondered how the routed the exhaust

Yes, there is lots of Donkervoot info at http://www.donkervoort.info

Is that healthy for the tire?

Not really. But as to how bad it is is open to much debate. My exhaust points at one of my rear tyres and that wheel is steadily going black! Given that my tyres tend to get quite warm anyway I'm not sure how much it matters.