The new arcs are set between the back-story elements of Wizard and Glass, and Little Sister of Eluria. I.e. way before the Gunslinger let alone Wolves of the Calla.
As has been mentioned some of the creatures and mythology described in the back stories of both arcs don't appear until the later books, but whether that is truly a spoiler though I'm not sure since a lot of it is only in hindsight (as Cyber says.)
If in doubt, I'd just read the rest of the novels first, especially if you're likely to do that at some point anyway. If decided to read the comics first though, I don't think it would spoil things that badly, but definitely read Wizard and Glass first.