"Indie" meant independent of the big publishers. Essentially, creator owned. So small publishers like Image and Dark Horse - as well as Oni IDW, etc -- could and should be called "indie." I just use "small publisher" myself.
Vertigo doesn't count as DC owns it, and most, if not all, the properties it publishes. Actually, who does own titles like Y and DMZ? I know DC owns Sandman, Swamp Thing, Constantine (and Watchmen, V for Vendetta), etc. Vertigo seems a mixed bag rights-wise, but it is a DC imprint and so isn't an "indie".