Can Restylane dermal filler be used for the vagina?

Restylane to the labia majora is an off-label use. With any filler injection, there are risks, including, but not limited to bleeding, bruising, swelling, asymmetry, under or over-correction, damage to surrounding structures, and accidental blood vessel injection that can lead to decreased blood flow to the tissues, causing tissue destruction and wounds. Some plastic surgeons utilize fat grafting to the labia major, which also carries risks. Please speak to a fully trained plastic surgeon about this issue for further information and evaluation.

Fillers can be used off-label in other areas of the body. The principles are the same.
There is always a danger of problems with fillers, and they are similar regardless of where they are used. In the labia, it would not probably be blindness, though, since the vessels in the area do not go directly to the eye. However, there is still a risk of filler entering a blood vessel, which is what leads to some of the problems you mentioned. A skilled injector is the best one to choose for any injection, and one who knows what to do if there is a problem.