Rockets

Yes. It's only two or three pixels, but rockets will damage ground units even if it is not a direct hit. The effects diminish as units are further from the blast center.

Nuclear rockets have a 50-km blast radius, and, as far as I can tell based on my own recent experimentation, the damage effects diminish very little further from the blast epicenter.

Is blast radius of normal rockets affected by its level?

I would not think so, for no other reason than that would require additional levels of programming. But I don't know for certain. I rarely use L1 through L3 rockets, simply because I am usually hiding my ability to produce them until needed, i.e., when someone else starts spamming the damn things. I do the research, and I maintain plenty of L5 industrial complexes with L2 air bases that are capable of producing them quickly if and when I need them. Now that rockets have a daily oil upkeep of 100 tons, I especially do not want to keep a bunch of unused rockets in inventory.