Very cool...I will certainly check out his YouTube page later today.
Fortunately, Kunos has established some very good relationships with car manufacturers. This isn't necessarily anything special - I'm sure many game developers develop similar relationships with manufacturers. So, when they are granted a license on a particular car, some companies roll out the red carpet, send engineers to Vallelunga with test vehicles for Aris (and others) to drive - take all sorts of measurements...everything you would expect a sim company to do.
I doubt every car manufacturer is that accommodating. Especially if there is going to only be 1 car from them in the sim. Or maybe some are just against sharing engineering data. I'm also making assumptions here. Again, I only know what Stefano, Aris & Marco tell us. Sometimes it's like, "Woah!! They really did that for you guys? They went into that much detail! Wow..." but, we don't hear that all the time. It doesn't mean that it didn't happen - maybe Kunos people didn't feel like going into it because they have real lives and don't want to live on the forums...
I think it would be really cool to be a fly on the wall for a single project...Take the Porsche project, for example. I wonder what truly goes on in those development sessions together - testing on track and testing on Assetto Corsa. It's probably pretty cool. Again, I'm sure every sim developer goes through a lot of the same stuff -- Kunos happens to be very lucky and have their headquarters inside a race track.