No, Rockboy is not included in the Sansa Clip version, only target with a colour screen and additionally to this the H100, the M5 and the Archos Recorders have it.
The plugin needs special "LCD drivers" for certain screens (especially greyscale and monochrome screens can work differently internally but most important for this case). This is also one of the reasons why the greyscale Ipods don't have Rockboy yet, even though the bigger ones have the same screen size as the H100 and M5). I guess that this is the problem here.
Seeing that Rockboy is... well... visible on the Archos screens which is similar sized as the Clip screen, I think it should be possible if the Clip has enough buttons for the controls. But it probably needs some work still.