RAD hardening deals with bit flipping due to event upsets. RAD hardening uses redundancy and distancing to reduce the likelihood of bit flippinp\g.
Although I have not studied the damage mechanism of EMP in detail, a simple search reveals that it works by generating current or ESD which can damage (permanently) computer equipment.
A nuclear EMP is the abrupt pulse of electromagnetic radiation resulting from a nuclear explosion. The resulting rapidly changing electric fields and magnetic fields may couple with electrical/electronic systems to produce damaging current and voltage surges.Excerpted from Electromagnetic Pulse
In the 1980's I had the opportunity to design spacecraft gear which had to be rad-hard (in the proper sense), and some years later I was designing industrial/consumer gear which had to meet FCC high-voltage discharge (ESD) susceptibility requirements. In my earlier comment I conflated the two categories, which was incorrect, and I thank you for calling me on it.