Continuity mistake: In the motel chainsaw scene, before the Colombians pull out their guns, there are several food containers, a bag of cookies and a soda can lined up neatly on a table, seen in multiple shots. After the skirmish, Hector pulls the chainsaw out of its box and Tony is leaning against the table with the items now all scattered in different positions. A few minutes later, Manny shoots his way in. You can see the table in multiple shots and the items are back in their original positions.
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.