It's been a few years, but I have been to DL in August. It was hot, but not unbearable like it can be in WDW in the summer. (But then again, I'm from Hawaii where it's often hot and humid, so maybe I'm more used to it.)
As far as crowds, it probably will be crowded, but a benefit is that there will most likely be two showings of Fantasmic, unlike the off-season where there is no Fantasmic, except maybe for weekends. Park hours are also a lot longer, so you'll be able to accomplish a lot.
I would go for it!