Where are you getting the nectar from? The brands around here that carry the fruit nectars are full of junk, and yes I'll admit I am picky. I have found frozen mango chunks at Super Targets, that maybe a better direction.
VPC
Saw a add in COSTCo's. I do get some of my 100% juice from them BUT I have not looked at the ingredients as yet to see if there are any sorbate / preservatives in it.
Sorbate would be one of my concerns. High fructose corn syrup would be another, I'm just not convinced I want that in my wine. Good luck mango's make a great wine, both still and sparkling. One of our local wineries makes a terrific one: http://www.floridawine.com/wine_selection.htm
VPC
I have used frozen juices with both sorbate and high fructose corn syrup. They were slow fermenters but made decent wines. One that my wife and several others like is Welch's Frozen Concord Juice Cocktail, which I have made at least 3 times. The result is a "blush-type" wine.
My advice would be to make a small batch and test the result.
I don't fret over losing a wine such as the Welch's when a 5 gallon batch costs less than 10 bucks!