That's a different situation again: Your buddy left, entered somewhere else and got busted coming back because whatever crappy 1980s IBM mainframe that runs your immigration system noticed he left the country days after the fact and flagged his passport.
Maybe but that isn't the point. People are saying Ralph can't go to the UK. I think even Null said it on MATI.
I'm not an immigration lawyer but I really don't see why not. The rules on the UK governments pages don't seem to bar him.
I doubt a DUI or something would matter at entry time. It would be more of an issue if you got into trouble in the country as failing to declare something you are required to would mean you entered the country illegally.
If you've ever been through Heathrow you know it looks like most of the terrorist generating nations of the world are having a conference in the departure area. Being from the US and looking like a senior citizen will probably mean that Ralph gets a single look from the border officer and then waved through. They have people with hooks for hands to deal with so no time to quiz a fat old white guy on which of the premium burger outlets he intends to visit to make sure he's legit.