Yes, hydrangea buds will be damaged by a late hard frost and the half of the shrub exposed to the most wind would be the half most damaged by a frost. That does not explain the wilting however. I suspect there is root damage to the two sad looking plants most likely from a mole or vole. Look for entry holes near the base of the plants or feel around for runways of soft earth. A mousetrap can capture the shrews or voles but you will need to do some digging to set a proper mole trap near your shrubs. Go ahead and cut back the wilted parts of your hydrangeas if they do not perk up after a good soak.  You may end up removing the entire shrub is the root damage continues but the good news is that there are so many great new hydrangeas available now. You can even grow the more compact hydrangea varieties (The City Line series, Endless Summer) in large containers where they will be safe from burrowing pests. Keep growing, Marianne Binetti