I would veto. Aside from the obvious disparity of a 1st rounder vs a 6th rounder....
1. Pujol's risk was known coming into the draft, if he was that "concerned" about it he should have just drafted someone else.(if its a keeper league its a veto anyway regardless) This makes it smell fishy, if you think Reyes is going to have a terrible season you don't take him with the first pick and then sell him to the lowest bidder in the second week of the season. You simply draft Hanley, or Arod instead.
2. In my mind you can't justify selling low on an injury risk if your getting another injury risk in return. If he was really concerned about the injury risk then he would have traded for someone who is a "sure" thing, and while guillen hasn't missed a lot of games the last two seasons, anyone who owns him knows he is somewhat injury prone.
Both of these things make it smell fishy to me, if it was two people I knew and I knew there was absolutely no collusion I _might_ let it go, two people I didn't know that well? Veto absolutely. Pujols is a game-breaker, hence his first round status, even if he plays hurt he will be by far better than guillen.