I get where you are coming from. My parents are in education too so we planned our wedding on spring break to ensure they could easily make it.
However, I think a big thing to remember is that DWs aren't the typical Fri, Sat or Sun weddings. Everyone here gets married on different days- like I said, ours was a Thurs.
I think you will aslo find that when you are on vacation, you don't even know the day of the week. Every day is a Saturday!!
So did you already change your date from 5/14? If so, you can just easily send out a postcard from vistaprint (because I think they are really cheap- even free) just noting the date change. No big deal cause you got some time! I had to bump our date up a day and no one even cared. I wouldn't worry to much until you HAVE to.