There are plenty of people running Rohloff hubs on non Rohloff specific rims, so I doubt if that is the main reason for your spoke failures, most likely something to do with the wheelbuilding.
<nods> Sure does, for the factors Dave mentioned and more. When I build wheels on 406mm rims, I use a steel rod as a die to gently form the spoke ferrules for a better approach between rim and hub.
For a nice photo/thread showing an acute spoke/nipple angle on a Rohloff-hubbed wheel, see:
http://www.thorncycles.co.uk/forums/index.php?topic=2056.msg9883#msg9883 The rim does not have "aimed" seats, and apparently Sapim Polyax spherical-head nipples weren't used. As a result, the nipples seat vertically, while the spokes bend at the threads, over-stressing the spoke threads and the ends of the nipples.
Best,
Dan.
