Audio problem: When Tony is about to kill Frank, Frank says "Look Tony, please don't kill me." You can see that he is not saying anything. His audio is obviously added in by Post Production.
Audio problem: At Tony's interrogation at the Immigration Office, the voices of two of the INS Officers are shoddily dubbed over. This error is made even more noticeable by the fact that the first officer has been replaced by the distinct voice of actor Charles Durning. The other officer is voiced by Dennis Franz.
Answer: It's unlikely a set up. Tony is supplied with money and guns to defend himself. If this was a setup, the toad would've had more details. He would've known Tony had backup with guns and they would've waited to ambush them. Also makes no sense for Omar to put himself at risk without a legitimate opportunity to make cash. Frank knew about the deal as he supplied the buy money. Omar seemed loyal to Frank. Why would he send some low level thugs to be set up losing his boss' money in the process? All he would do is lose trust and be suspected.
Omar was an informant. He wasn't loyal to anyone. Omar's driver is the one that suggested to send Tony to the Colombians. And I think Omar knew the Colombians were shady, and that's why he sent Tony. It was, in a sense, a setup.