If every other Denver running back somehow got injured before the draft, Dayne would be going in the second round of most drafts. Even he would be a 1,200+ yard, 10+ TD back as a full season featured back in Denver's system.
My reservation about Dayne has nothing to do with his ability. The problem is that Denver has a stable of running backs, none of which is the clear cut starter. I'm only sure of one thing in that offense; one running back will compile 1,000 yards in 2005. Problem is, it could be (in no particular order) Bell, Griffin, Anderson, Dayne, some relatively unknown already on their roster (it's happened 3 times in recent history), a free agent yet to be signed by Denver, or a running back they pick up in the draft (yes, Shanahan will draft a running back).
I just can't see spending an early round pick on ANY of Denver's running backs. Even with Bell, the most likely start in Denver (IMO), there is a huge risk in drafting him.