I first saw him as a space hippy. So him playing cops and rednecks are what seems odd to me.“Truth is stranger than fiction, but it is because Fiction is obliged to stick to possibilities; Truth isn't.”
I'm sure there are plenty of people who looked like Charles Napier that were hippies. But, imo, a casting director shouldn't say "Well, it's possible that a person who looks and sounds like this could exist." There job is to cast actors who fit roles.
I think that if I had never met Charles Napier before, and I had a chance to see him and hear him, I'm pretty sure that "hippie" wouldn't be the first thing that would spring to mind. And in episodic televsion where you have a guest star pop in for 50 minutes only to never be heard of again, you only have that first impression. You can't spend multiple episodes fleshing out the character, letting the audience get to know him. So you say "Does this guy look the part? Does this guy sound right for the part?" and you roll with it.
He went on to have a 40 year career playing rednecks and hardass tough guys, with nary a space hippie role again.
I'm sure casting directors in 1968 had a different view of "hippies" than people today. They probably saw the real deal in the Hollywood of the late sixties.