is it possible for units to dodge a nuke

If they are a fast unit that is moving, then it is possible

Naval units can, because if there is nothing at the target location to trigger the detonation the nuke just sinks to the bottom. If the target does not move however no naval unit is fast enough to get out of range during the flight time.

Planes do travel fast enough to get out of the blast in most cases.

Otherwise There are no ground units that can move fast enough to get out of the way of a nuke.

The only chance would be if they were already close to the edge of the 50k blast radius, they might be able to get outside the blast zone in time. They definitely cannot travel from the target location to a safe location during the 20 minute or less flight time of the nuke.

so if i were to nuke a big group of enemys that was aimed directly at them they cant dodge it

Likely not.