In this context "rock lovelies" almost certainly means attractive female rock(-and-roll) musicians (or possibly attractive female hangers-on of rock musicians), so "rock" is just the adjective meaning something like "relating to rock-and-roll music".
I take it the Oxford Pocket Dictionary was meant to be a pared-down alternative to the Oxford Dictionary of English and the Oxford English Dictionary, squeezing as much information into as small a space as possible. The extended definition for this sense of lovelies given in the OED, 2nd Ed., is
absol. or sb. Now usu. a woman or girl of glamorous loveliness, esp. one who takes part in an entertainment or 'show'.
The OPD has apparently chosen to convey the emphasis on an entertainment/show connotation through use of an example of a common type of entertainment/show, but unfortunately chose an example that is not actually in common usage and that is therefore ambiguous.