Hmmm...interesting question Mark. I think Ragtime has a lot of blues in at...at least the stuff that was coming out in the early 20th century...(and of course blues and ragtime are the foundation of jazz) but it's also a real hodge podge of other musical elements like fiddle tunes from the Buckdancer era.
The 3 things I find that seem to define the ragtime sound for guitar are ,(a) the syncopated melody and rhythms around the alternating bass; (b) a lot of swing and bounce to the playing and feel (-you can take any alternating bass song and give it a ragtime feel), and breaks with single string runs, (c) and walking up and down bass lines connecting the chords together.Also, a very good article here on the King of Ragtime Guitar.