Very interesting...haven't explored whether they are legal in Idaho. DUI roadblocks are unconstitutional in Idaho per a court case decades ago, but don't know about interdictions. One has to wonder how a DUI checkpoint/roadblock is unconstitutional but a drug interdiction checkpoint/roadblock would be allowable.
Certainly, a person carrying a weapon can be expected to be treated the same as he would in any other traffic stop, but it may be different if they're pulling people out of cars and running a drug dog around their vehicle and notice at that time the driver or passenger was carrying. They'd probably want to do all the same things that happen when they encounter an open carrier any other time - secure the weapon, identify the person, run them for wants/warrants...and react the same way when the carrier exercises his right to remain silent, not show ID, etc.
How did the contact go? It'd be interesting to hear about your experience, and see if any criminal cases were made as a result of the interdiction, particularly if the constitutionality of the checkpoint/roadblock is challenged.