Yes you can:
http://www.nectar.com/rewards/generalSe ... ROM0006694
I recently got myself a Nectar card as the only supermarket in Winchester town centre is a Sainsburys and I was using it daily.
Looking at the rewards, I think they are pretty dire. 4,700 points for Thorpe Park entry? That means you'd have to spend £2,350 in Sainsburys supermarket! Or £2,000 if you reuse your bags :lol:
Only £10,000 for an Annual Pass!
I guess it's not that bad if you collect elsewhere than Sainsbury's but Tesco Clubcard is much better for these deals. I hope that answered your question.