Reverse grip works best with short swords and knives. Longer swords, close to the size of a standard lightsaber would be harder to wield in a reverse grip. However, since these are lightsabers we're talking about, and they have a difference center of balance and different weight simply because only the hilt has weight, it might not make a difference.
The only downside of a reverse grip in this situation is that he is leaving his front undefended. Then again, he is a Force user.
Anyway, before we discuss his semi-realistic application of the reverse grip, we must first discuss Maris Brood who is using lightsaber tonfas. Anyone who has ever practiced with tonfas before will tell you that she will dismember herself within the first few seconds.
Basically, my point is that it's a game about people with magical powers, it's not meant to be realistic.