Yup they sure are, I recently redeemed a Terry Hill signature card from the NRL 2000 series by Select. Emailed Di at Select to confirm and sent it off, no probs.
FYI, just received a reply to this question from Di at Select, she indicated that pretty much all the NRL cards are available via redemption. If you pull a redemption card from a box then u should be able to redeem it.
Yeh not sure about NRL, but there are certain AFL cards that can not be redeemed anymore, Like 2000 and 2002 prem predictors, some captians (bradley), etc etc.