I thought it was Paul Frees, but he died in 1986 so that can't be. But the voiced B. Louie? The voice talent isn't listed in the credits. I was sure it was Paul Frees.
shareAreed! Man, I could SWEAR it was Paul Frees, the voice of the guy that did the Haunted Mansion voice over at Disney.."Welcome, foolish mortals, to the Haunted Mansion. I am your host – your "ghost host..."
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I'm your average ordinary everyday, jorgeegeetooo!
It's actually faintly possible Paul Frees could've still did Louie's voice. UHF was in production for years before it got the green light. For example, the main parody is Money For Nothing (from 1985) and that was already 4 years old. It's about tied with "eBay", or perhaps even a little more, as the oldest song (at the time) Al parodied.
I think most of the actual filming was done in 1988, so it's still kinda unlikely if Frees died in '86, but it's possible. All he used was his voice in a few scenes, so he wouldn't have had to do alot of retakes.