We print hundreds of vests a week, and don't change a thing. Gas dryer, same speed, same temp, no additives. That being said, probably 99% of them are mesh vests. There have been some chepo vests over the years that have shriveled up by the time they exit the dryer but they have not been mesh and just felt cheep. What is the brand of the ones you are going to use? Another thought is you can always call the manufacturer and see what their flash point is.
If the customer only wants black on them there shouldn't be a need for a flash... That only seems to screw things up!