Given the fact that teams are not required to select players in the supplemental draft essentially makes it very different. Eligibility for the supplemental draft indicates something went awry (normally legal and/or academic), with the player, affecting eligibility for the regular draft.
Regardless, Pryor was not projecting to be an ideal pro QB. Among character issues, there were question on his accuracy, his ability to read defenses, and according to most mock drafts that year (had he declared), he was not projected to be a high draft pick to begin with. Even then, there was talk of a position conversion.
The fact of the matter is that Pryor's Wonderlic score was a pretty good predictor of what kind of player he projected to be and while he was drafted as a QB, he was traded or released 3 times before he actually did convert to receiver.