Well remember this is a two part thing. First off the NFL doesn't like having their stuff used to send messages, largely for backlash fear there's always somebody out there that thinks message X is stupid and any implications that the NFL supports it could cost money, this is really the part the NFL is objecting to. Then there's the image thing, who owns your face, and in that regard the NFL actually does have a certain level of ownership of Smith and Dungy, they're both members of the coaches association, thus allowing the NFL to sell their names and images (like for EA Sport's Madden series, there's a reason Belichick is always listed in Madden as "NE Coach", he's not a member of the CA and refuses to sign EA's paperwork) and apply whatever rules are in the CBA to their public appearances.