Douga are not machine drawn ! Even in anime using
only CG, douga are still hand-draw and then
scaned. Only the coloring is made by computer.
(so there is douga but not cels).

As of my definition of genga... it's not mine.
It's what people working in some studios
explained me. (and I don't claim to be able
to recognize a genga from a rough sketch even
after the studio's explainations. It's far
easier to recognize what is not a genga...)

Cheers,
Y.S.