i really don't see what the problem is, as it's usually the problem is when you go the other way round and try to run a non digital bulb in a digital ballast..
i'm sure you know what the issue with digital ballasts and non digital bulbs are by now.. for w/e reasons, the manufacturers of digital ballasts have them firing at a much higher frequency then older mag ballasts did.. this higher frequency will then reach the bulb, and causes vibrations from what i've read of them, and it's these vibrations that cause regular bulbs to fail in digital ballasts..
so, i don't really see a problem in running a digital bulb in a mag ballast, but maybe some one else will chime in with some more info..