I am sort of being forced into having my wedding on labor day weekend. not getting into that again..but I also had a freak out about it too.
1 - peak hurricane season - with the exception of my dessert party, the wedding is indoors (WP) and so is the reception (ADH), if there is a crazy hurricane like Sandy where all highways were shut down in NJ I have been told by other brides DFTW will work with you to reschedule (hopefully that is true) I am also going to purchase some sort of wedding insurance for that.
2- heat - once again, DP is the only time thing that would be effected and its 8pm, so probably a little cooler at that time. Heat at the parks is a different thing, but then again you can always get some ice cream or go see a show or something to cool down. My DF HATES the heat but apparently he thinks it wont be a problem for him when I tell him how hot it will be.
3- crowds - i have been to disney during christmas so nothing can compare to those crowds in my opinion. I have not been to Disney in the summer, so maybe its comparable and I guess I would rather be on line in cooler weather with a ton of people than warmer weather. but if you plan your trip out with fastpasses etc. you should be fine.