I had not heard of this, so I tried to look it up and found no restrictions on trading players for draft picks in the CBA. It's 300 pages long so maybe I missed it, but if you want to skim through it the complete text can be found here: http://images.nflplayers.com/mediaRe...Searchable.pdf
I think there might be some confusion because this year's draft occurred during the lockout. so you couldn't draft a player and then trade him for another player (like the Rivers/Manning deal), you couldn't trade players to get more draft picks. In fact you couldn't trade players at all.
Now that the New CBA is in effect I would assume you could trade a player for anything including other players, draft picks, cash, Denny's gift certificates and a bag of footballs.
If anyone has information to the contrary, please post a link.