I think The Swedish Chef still has human hands. I thought that he did in The Muppets Wizard of Oz. He usually just has muppet hands in promotional pictures where a poser puppet is used. It's probably easier for a poser to have muppet hands than real hands.
The only times I can think of where he had muppet hands in actual productions (and not pictures) were in various full-body shots where it would have been impossible for a performer to use his real hands for the chef (because the performer wouldn't have anywhere to hide) and in the first episode of Muppets Tonight (I don't know why he had muppet hands there).
Here are all full-body shots of the chef that I know of:
-in the Linda Ronstadt episode, where he makes champaign and ends up popping to the sky, landing in the following Muppet News Sketch.
-in the bike riding scene in The Great Muppet Caper.
-I think he was seen in full-body view when the muppets were climbing down from the roof of the mallory gallery in The Great Muppet Caper.
-There was a full-body shot of him sitting on something in the plane at the end of The Great Muppet Caper (although in that scene it would have been easy for a performer to hide from view).
-during the end credits of The great Muppet Caper, there is at least one full body shot of The Swedish Chef (I think there were more than one).