My DS15 doesn't play football, but he IS in the band, and they start practicing at the beginning of August (the second week, I believe). Band (ours anyway) is a big deal here. My DS would not want to miss it for anything.
That said, when he was a freshman, I wouldn't let him miss any of the practices because he was new and didn't know anything yet.
Now that he is an "upperclassman" and knows how things run, I may feel differently about him missing a few days, but he still would not want to miss. The directors strongly encourage parents to plan vacations accordingly, but they would never kick a kid out of band for missing a couple of days of summer band practice. I'm not so sure that football runs the same way...something tells me that your son might sit on the bench.
I'd try to change your dates.
Our band starts practicing in mid-July. Unexcused absences, which a family vacation would be, could very well get you kicked out of the band here. The band schedule for next summer will be out within the next couple weeks (if isn't already, I haven't checked) and vacations are not considered an acceptable excuse to miss. Everyone in the band knows pretty much when stuff happens (band camp, drill camp, etc.) so even without the schedule you know NOT to schedule any vacations after mid-July.
Our band is internationally renowned because of the style of band we are, but I know that marching band here is NOT what it is in the mid-west! 


