Ahem. Well....
<Only certain kinds of radiation (not electromagnetic) can cause materials to become radioactive themselves.
In terms of significance, you're correct but as you may remember, phil and I we're discussing x-rays stimulation of gamma ray emission from certain isotopes a while back. Also, gamma rays (which is electromagnetic) can alter light nuclei by 'knocking' off neutrons or protons.
So, it does happen but it's not a strong effect.