From my experience this past weekend for the Princess Half:
Expect Uber to be a likely & reliable option for the 5K & 10K days AS LONG AS you request one early. I requested my Uber at around 3:50/4:00 am on Saturday for the 10k with no issues. Keep in mind, even for Orlando, Uber's are not as readily available at that dreadful hour.
I would NOT use Uber as an option on a half marathon or marathon day unless you're going way early, like 3:00 am. I tried to request an Uber at 4:00 am. None available!! The roads start closing around 4:45/5:00 am, so even if you drive leave EARLY. I barely made it to my corral in time on Sunday. Heavy, heavy traffic on half marathon and marathon race days.