ideal movement for a shrug is actually shrugging slightly back. straight up and straight down is the gym method, but to hit the bulk of the upper traps. lean forward slightly and shrug as if your ears are about 3 inches behind your head (bad visualization sorry) but since most people shrug to their ears...its all i could do.
i do mine on a tbar by bending just slightly forward and the bar travels perfect. blows em up.
the whole rolling shoulder thing......put it in the closet with behind the neck ANYTHING.
I have honestlt rolled for many years and suffered no injuries. However, I recently stopped in favour for up and down after reading a similar post to this.