As long as the charges were dropped, he wasn't found guilty of anything, and he gives full disclosure, he should be okay.
I had a felony arrest for a weapons charge awhile ago that when my fingerprint records came back plant security pulled my badge. Took me two weeks waiting outside the gate to get talk to the head of security. It was a single action 22 cal pistol, unloaded, locked in the trunk, which is how I thought you were supposed to travel with a firearm (just finished a plant and was heading home). All charges were dismissed, but as the plant security told me his report only said "felony-weapons charge". For all he knows it could be for a Mac-10. I had copies of everything in my briefcase so they let me back in.
Then they tried to fire me for not disclosing the incident when I took the job. The question then said in the last 5 years..., so they went back and saw that the other 3 times I had been there I wrote everything up, but it was now more than 5 years later so I hadn't bothered. Which is why I say make sure he doesn't try and cover anything up. Good luck to your friend.