Other mistake: In the scene that begins with "Three Months Later" where Tony and Manny are sitting at the table near the beach watching the girls in bikinis walk by, Manny is attempting to explain to Tony how to pick up women by explaining what "women in this country know and understand". After Manny sticks his tongue out to demonstrate and Tony asks Manny "what the f*ck was that, Mayne?", if you watch Al Pacino's lips as Steven Bauer is talking, you can see Al's lips moving in unison to whatever Steven is saying.
Other mistake: When Tony pulls his arms down from the shower curtain, there are no chains on either of his arms, and at no time do you see them fall in front of him.
Other mistake: Manny is shot in the scene in the motel, but when he is in the bed with the naked lady, there is no sign of any type of bullet wound in his chest, side or arm.
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.