I realize it's off topic, but I still want to know. If Rocker is a hidden trait, it has to do something. If it does absolutely nothing, then nobody would even know about it. This is the first I've heard of a Rocker trait. How would it be similar to Virtuoso? What would be the point?
Well, according to the official description,
'Sims with the Rocker trait will have a natural feeling of the Rock stardom". I also believe it does nothing, other than being quite similar to Virtuoso (i.e. if the children of the Sim in case don't have Virtuoso and have the Rocker, they may still raise the music skills at a faster rate). I cannot confirm, though. Once I had a Sim in Music career, at level 10, but unfortunately both of her children had Virtuoso trait, thus (maybe) hiding Rocker trait's advantages. I'll be sure to test this in my legacy too, assuming the founder has the One Sim Band lifetime wish, and the Music career goes along greatly with it. Until then, I found
the trait's Sims Wiki page, it is on the guide too,
right at the bottom of the Traits page. Other than that,
discussion about it on the official forums, and, of course,
on our own. So after, all the research it's the thing needed to unlock the hidden skill of Air Guitar. Hm, interesting if you ask me.

P.S. I believe we should continue the discussion on the page I linked to. Thus we won't be off topic anymore.