One is generally asked if one has been convicted of a felony, a false arrest with no charges lodged doesn’t have to be reported unless one is being vetted for high security type jobs.
This guy is a registered nurse.
Depending on the state, you have to report any arrest (regardless of convictions) to the licensing board. From what I can tell in a quick search, Virginia does require it.
Even if he doesn't report it, it will show up in a criminal background check -- which is done for all nurses these days, due to government requirements for people handling scheduled drugs. He might be able to get the record expunged, but it's not always successful, even if he gets a legal order to do so.
Depends on the field. Many companies in my field check for arrests as well as convictions.
Arrests can be explained in some cases and would give the person a chance to explain. In other cases they won’t care.