I can't say definitively that non-TSA teams will not be working be working at or near TSA checkpoints - currency detection teams and other teams could certainly be working checkpoints or other parts of the sterile area.

As to your question about the 4th Amend: I personally do not see how such a search would be permissible.

However, I can easily envision a scenario where a drug detection dog alerts while a person is walking by so the handler notifies a second officer who makes contact with the passenger and during the course of that interaction the second officer, based on his experience and training, develops a reasonable suspicion the person is violating a law due to the person's demeanor and responses to questions. The interaction then escalates to an investigative stop. During the investigation, the second officer asks if the person would mind if a dog inspects his luggage/person. If the person says yes, the dog alerts again officially and its off to the races. If pax says no, then the officer becomes more suspicious and increases the intensity of the investigative stop until he can reasonable justify a search of the person (and every decent cop can do this - its what they are trained to do; its their bread and butter).

I share your concerns.