Sam was a junior fiddle champion, and he was advised by Bill Monroe to stick to fiddlin' when he demonstrated his mandolin playing to Bill. So I'm curious why has Sam not professionally played his fiddle much? (I assume that Sam became a better player on the mandolin than the fiddle.)
IMHO, Sam HAS played his fiddle quite a bit. In fact he arguably has one of the most distinctive styles and fiddle tones in the genre. Just as it's quite easy to pick out Sam's trademark Hoss chop, his fiddle licks are often a dead giveaway on the many recordings he's on.