Virgin Atlantic's normal airline code is VS. For some reason, Avis used to use VF for Virgin; in the US, they often denied that Virgin was a partner and I had to educate them each time, politely but firmly

. When they entered 'VF' in their system, sunshine broke out

.
Anyway, my VS number is in my Avis profile and miles credit automatically. I just checked that my two rentals from two weeks ago in South Africa were in my account - yes, they were.
So far as contract rates are concerned, I guess you would know if you were on a contract rate - a little like no-miles prices for air fares or hotels.
The reason I think the answer to the question is Virgin Atlantic is twofold:
- 1,000 miles per rental (for me, at least)
- VS still offer transatlantic awards based on 40,000 miles - most US carriers and BA ask for 50,000.
So one rental = 1/40th of a London-New York round trip. Not bad.