Open Mike said:
"One the way here we listened to
http://en.wikipedia.org/wiki/Goebel_Reeves who claims to have taught
Jimmie Rogers and Woodie Guthrie to yodel. a.k.a "The Texas Drifter" he had a huge variety of yodelling styles he sang"
Goebel wrote Hobo's Lullaby which Guthrie recorded, so there may be some creditability there. Goebel's recording of the song has a couple of extra verses and yodelling as well but it doesn't seem to fit to my ear. In any case it's his song so who am I to judge!