I'm using v01.02.15a on my Clip+ and will soon install Rockbox.
It doesn't matter. Rockbox is its own stand-alone firmwware that (virtually) sits beside the OF (original firmware). It doesn't depend on the OF at all.
Last I heard, Rockbox only works with v 01.02.15 or older. So I don't recommend that you upgrade the player's firmware to 01.02.16, the lastest, until you find out whether Rockbox will work with the newest version.