You need to get two nuts on the other side, lock them together (unscrew one and screw the other one so that they are against each other and torque) then put your wrench on the inside one (towards the hub) and from there unscrew the one that is currently stuck. This is how I have to get frozen cones out.
EDIT: Do this at your own caution! You do chance stripping something. Oh, and you may also want to try putting some oil where that nut is to help.
Before you start using vice grips on anything, put a nut on the axle ahead of where you are going to vice grip, in case you do mangle something, you can twist the nut over the mangled threads to possibly repair what got mangled. Just a precaution.