I am generally not in favor of trade vetoes (as I'm sure some of you have noticed), but I would definitely consider a veto here. This is a clear situation of using an injured player to get healthy guys in return. Granted, sometimes people will trade for guys on the DL, but Team A was clearly not thinking this way.
This situation relates very much to how things are handled in MLB. Say Oakland (Team B) and another MLB team (Team A) were in trade talks involving Harden. Everybody involved knows of Harden's injury past, but they also know he is on the road to recovery and should return to action soon. Suddenly, Harden has a major setback and completely blows out his arm in a rehab start, but Team A does not recieve this info. The next day, the trade is completed and Team A only finds out about the injury when Harden reports. If I understand correctly, Team A has every right to file a formal protest to MLB against Team B because they did not properly disclose the status of a player involved in the trade. See what I'm getting at here?
Now, I don't know exactly how MLB handles these situations, but I think they have the right to rescind trades. I know a situation like this has happened recently with the Reds and Nationals involving Mike Majewski (http://www.washingtonpost.com/wp-dyn/co ... 02078.html
). I think the protest in still pending.
Anyway, back to your situation. I think this was a "poor-sport" moves made by Team B and the trade should be vetoed because Team A did not know all of the info.