I dont see why not. IF youre worried about drainage, you can put a "Drain" into the planting hole. Ive never done it but ive read about it. Basically you would dig the planting hole as usual, but then you dig down another 3 feet, in the center of the hole about 3 inches wide. Fill that with gravel, and it should help you get rid of some excess water.

I will say I have seen pics of fruit trees in raised beds. I have a pear and an evans cherry in the same sized spots, just not raised.

Ya,

Lovell is a full vigor rootstock and will not dwarf your nectarine. You can still keep your nectarine small though, you just have to prune it more often.

look at dave wilson nursery videos on youtube they use raised beds all the time when drainage is problem. His are about 2x2x1 ft i think. I was thinking of doing this for a couple of peaches as my ground is too wet and low for them I have found out.