I don't think it absolutely requires an offset rim, I just figured that, if it's good for a rear wheel with a freehub, the same reasoning should apply to a front wheel with disc mounts. It seems to me that the dynamics would be about the same only in reverse (i.e. the disc is pulling on the trailing "drive side" spokes in the opposite direction). I ran the numbers through Spocalc using the M756 hub and an Aerohead OC 32h rim, 3x lacing, and I got nearly equal spoke lengths for both sides, and a tension ratio of around 110% -- nearly perfect. With the Open Sport non-offset rim, the tension ratio was more like 150% with a 2mm difference in spoke lengths between the disc and non-disc sides of the hub. I think this means that the disc side of the wheel has to have 50% more spoke tension than the non-disc side, but I'm kind of new to spocalc, maybe I'm interpreting that number incorrectly.
I've heard that there are some disc-specific offset rims out there (Bontrager?), but this was just a generic Aerohead OC that most people probably use for rear wheels.