Maybe I'm missing something, but that does not make any friggin sense at all. A roots blower is a positive displacement blower, which means it moves the same VOLUME of air with every revolution. It shouldn't make any difference whatsoever what the incoming pressure is, the outgoing pressure would be greater. I can't see for the life of me how you would overspin it. It's not like its a fan or something. Can you reference me to a tech article of some kind describing this phenomenon?
Wait, did they put the s/c first and then the turbo? That might cause a problem, because the s/c might not be able to feed enough air to the turbo. But if the turbo is first, then the s/c, it should work fine, I would think, because the s/c is just moving the same volume of air as before, but with greater initial pressure. The pressure ratio shouldn't change, because the engine displacement is still the same. Like how on sequential turbos the first one is bigger to feed the larger volume of air to the second smaller one which feeds the engine. But then again, I'm just theorizing here, so who knows. Somebody got links to info on that?