Well, I have Ziatype prints made with digital negs that I'm prefectly sure no one could tell the difference, only if they weren't too perfect. Actually it depends alot on image size / paper and subject matter. I think traditional in-camera negatives still have the edge in the extreme highlights, but by not much. And simply - even if you're doing internegatives - the degree of control with digital can't be matched with film negatives.
What matters is, using whatever procedure that makes you realize your vision and artistically / technically satisfy you.
Good luck with Ziatypes, I like the process alot. Once you're addicted you can't print iron-silver anymore, the results are simply unmatched...
Regards,
Loris.