I have had take-out credit every time... although you might check the website for individual restrictions... as mentioned above, some places dont' allow points on Saturdays, etc.

As far as cash discounts/rebates go, I'm not sure. It may depend on what program you are using ot get the cash? You can still use coupons, etc. as the restaurant does not know your card is linked to iDine when you pay. What program gives you 20% back?