According to the TSA, film speed up to 800 is safe in the scanners at security for carry on. Over 800 they will hand inspect. Under they insist it go through. Same for checked bags. But for checked, you can buy a lead lined bag (get them at a camera store) to protect from the scanner.
I've never had a problem myself, but I have heard some people have. If you have exposed film (ie you took pictures) and you are really worried about them being ruined by the scan on the way home, then have them developed while at WDW. It's more expensive, but you'll be buying peace of mind. I've never heard of a problem with blank film being scaned, and then problems with development prior to return, only problems with scan both comming and returning and devolpment at home.