The verdict: According to his then mechanic Al Ludington, it's true. 

Ludington tells the story. "I think it was 1989 at Road Atlanta, at the Suzuki Cup finals. Ski had crashed a few weeks prior and broken his collarbone, and had it plated. He felt he could ride so we, we were working for Vance and Hines Suzuki then, went to Atlanta. 
"Ski crashed in practice in the back and came back with the plate the surgeon had used to put his collarbone back together bent and sticking up under his skin. I thought we were done for the day. 

"Ski sat on the pit wall, then took a hammer from the toolbox and started beating on the plate. He beat it flat again and he raced. I think he finished fifth in the race, maybe better."

Ends