The most important variable in all this is distance. How far away would the nuclear intercept take place?
For an intercept to be effective, I would think it would have to be on the order of 1/2 the distance to the moon or greater to achieve any real chance to introduce a deflection large enough to do any good.
If we assume that a nuclear intercept took place at that distance or greater, then most of the issues here would be negligible.
1. Radiation: If the initial explosion were >100,000 miles above the atmosphere, then there would be no measurable effect from the initial release. Then, anything that did reach Earth would be so dispersed as to be harmless. The only real potential for danger would be from any piece of the asteroid that reached the ground as a meteorite. I guess it is possible that one or more of these meteorites could be highly radioactive, but people could be warned away. So I don't see this as being much of a real issue.
2. EMP: The effect decreases by the square of the distance. It is a non-issue for any realistic intercept distance.
3. Atmospheric effects: Again, not if the intercept is at a realistic distance.
4. Bright flash effects: Well, brightness follows the same rule as EMP and decreases by the square of the distance. I haven't calculated the intensity but I doubt that there would be a problem.
Anyway, I guess it's clear that in my judgment none of these is a valid reason for not using a nuclear intercept. The real problems are:
1. How will the asteroid react to the explosion? Will it deflect or break up?
2. Can you deliver enough energy to do any good. The directional energy involved in an multi-mile wide asteroid is far, FAR greater than a nuclear weapon.
3. Can you get the weapon there? As I said, the intercept distance must be large enough so that the energy applied can do some good. This is a very solvable problem if there is enough time.
Anyway, just some musings from someone that gave a LOT of thought to this issue a few years ago.
Bob
