We have a 2012 Lexington, also with the fiberglass roof. Don't know about hail, but I would imagine it would hole up well unless the stones got really large. Even than, you would probably end up with cracks.
Also, you need to check the roof several times a year. Don't be afraid to walk on it, it's safe and won't cause any damage. You want to check for any hairline cracks that may have developed and treat them with a bit of caulk. I would suggest you get a couple of tubes of Dicor Self Leveling caulk. You can use it to patch any cracks in the old caulking and to seal or reseal any gaps or joints.
As for the cracks that may develop, I clean the area with mineral spirits and than reclean the area with acetone. Than a dab of the Dicor that I finger rub into and over the crack. Others use Eternabond tape to cover the crack. These aren't large cracks, just several inches or so long, but you have to keep after it.
Not every roof will crack, my 2012 has three small ones that I've found in 1 1/2 years. Supposadly, several years ago the roof manuf. supplied a batch of roofs that were not up to par and several started to develope cracks. Don't know just how many or what years were involved, but I googled info up and possibly 2011-2013 might have been involved. No fix was ever done and apparently FR won't cover it or acknowledge it.
In any case, I still think the fiberglass roofs are far and away better than any of the other roof materials out there, and would not even consider an rv without one.