I get forced-fed a lot of Drew Brees on television and sports talk radio living down here in Saints territory. One perception I have never had, watching or listening to the man speak, is that he was not a knowledgeable person. Just my opinion but I think believing Brees did not foresee his previous negotiated contract having a negative impact on the team's salary cap for player acquisition is a huge stretch of the imagination.
I am in northern Louisiana but I do know that the Saints fanbase were very apprehensive about Brees salary demands at that time. New Orleans/ESPN sports talk host Gus Kattengell of The Sports Hangover is a weekly guest on my area's afternoon radio sports talk show. Kattengell would often talk about the positive and negative aspects of meeting Brees' contract demands. He stated his show received many calls from the Saints faithful about the subject.
Basically, I cannot quantify Brees NOT knowing how his last contract would affect future roster decisions since A) he is (seemingly) smart enough to know better and B) the buzz surrounding him about his salary demands should have been too loud for him to ignore and not contemplate.
Perhaps I am completely wrong but I still feel 99% certain Brees understood his contract demands would likely cost the team key player or players.