Not necessarily true. I've blacked out the roof of my last few cars and have never taken a hit on it.
I thought of going this route once, but it never had the same gloss as paint. I wanted mine to actually look like it had a panoramic roof...weird part was when other Legacy owners asked if it was glass.
Might want to contact the manufacturer of the vinyl to check that. After I had my car vinyl wrapped, I called to see about waxing it and they advised me not to.