Pete, I am inclined to think that the Dobro players are pretending that they are Maybelle. She is imitating the "Hawaiian" style of the time. Sort of gently sliding up to chords. Little or no vibrato and little or no whine. I think it goes well with the songs in which it is used.

By the way. There used to be a gadget called the "Hawaiian nut raiser" advertised. Oh why, oh why didn't I get one when I had the chance?

Murray