Yes I realize that but I am assuming that any trade the Saints make for Butler would involve them hashing a deal out with him in advance and then Butler would sign the necessary paperwork to consummate the trade. Sort of a "sign-and-trade" situation.
As other members pointed out, I just don't buy the idea of a nudge nudge wink wink agreement being part of this deal. Even if the Saints and Patriots are 100% honest with each other, some other team could step in and make a monster offer to Butler and foul the whole thing up.