The fact that an informant gets a benefit by setting you up and testifying in court is something that effects his credibility and pointing those things out might convince a jury to disbelieve that informant. If the undercover agent was present during the "sting operation" won't his or her testimony be sufficient to convince a jury that the person delivered the drugs. Yes a person can be convicted on the facts that you gave but it all depends on what is presented to the jury.
The short answer to your question is yes.
Ms. Berjis is licensed to practice law in the State of California. The laws of your jurisdiction may differ and thus this answer is for informational and educational purposes only and is not to be considered as legal advice. Since all facts are not addressed in the question, this answer could change depending on other significant and important facts. This answer in no way constitutes an attorney-client relationship.