I wouldn't do it. During medical school I did a rotation in Asheville, NC. While there I visited the smoky mountains which are just east of you. Many of the trees on the tops of mountains have been dying. There were only young ones living. I was told that a major cause of the mature trees dying was pollutants in the rain and even the clouds. Would you want to add these to your tank? IMO, you might be able to get away with it once if it is a true emergency but I wouldn't do it regularly.
Rain or melter snow water with a pH of anything other than 7 means that there are other chemicals in it (i.e. pollutants). I would get that ph meter calibrated properly or use another method.