People always become critical of the GM when a draft pick doesn't pan out. It is not an exact science, however.
The pick of Flowers was a bad choice, but only because he was taken with a late first round pick. If I remember correctly, the general consensus was that he was a late 2nd round or 3rd round pick. The Bills (Wade Phillips) were wowed by him at the Combine and "reached" to take him.
This didn't necessarily have much to do with John Butler and the scouts. All of the NFL teams have reps at the Combine and their overall lists are about the same. They could have different opinions about a player based on their needs, how they'd fit on their teams and what came out of the interviews.
So, again, the worst you can say about the Bills' selection of Flowers is that they took him too early. Had they not taken him, another team would've a little later in the draft. He just didn't make it as an NFL player.
You can apply this same logic to the drafting of Mike WIlliams with the 4th pick in the draft. On everybody's board, he was rated high. Had the Bills not taken him at #4, he would've been taken at #5 or sometime soom after. He just turned out to be a bust with the Bills. You can't really blame TD for picking him.