I just started laying fiddle this year (I've played guitar for years though) so I don't know that much about the roots of Old Time. I've always thought of Old Time as traditional American tunes; separate from Irish, Scottish and French tunes and pre-bluegrass. There's often not much ornamentation in the songs but as with all rules there are so many exceptions...As for the pioneers, I'm not sure, but this link should help... Old Time Music Home Page Hope I got the hyperlink OK.
I don't know if there are any fiddler's who stick to real "Old Time" these days. My favourites are guys like Mark O'Connor & Sam Bush. However, you certainly couldn't peg them as Old Time.

Dave T