For example, let's say that the dog is not sufficient probable cause. Consider the cases:
1) drug dog indicates + suspect driving erratically
2) drug dog indicates + "I just have a feeling"
Am I correct that 1) might be PC but 2) could not be, no matter how accurate that officer turns out to be in practice?
(In case 2, the dog's finding more drugs than the base rate would not validate its accuracy, as the results are being pre-filtered to have a very different distribution.)
So rationally, the cop's "spidey sense" is indeed evidence. The question I posed to you (and whoever's reading) was whether it counts as legal evidence. And it's my understanding that, no matter how good your spidey sense is, it does not become PC in a legal sense until it is articulable. As Thomas Moore said in A Man for All Seasons:
"The world must construe according to its wits; this court, according to the law."
Yes, but that hurts your argument rather than helping it. The drug dog does not, by itself have to clear the probable cause hurdle. Rather, the totality of the circumstances has to yield probable cause: https://en.wikipedia.org/wiki/Illinois_v._Gates.
So say the base rate for carrying drugs is 10% in the population. The police, based on their suspicions, pull over a population of people where 40% are carrying illegal drugs. Then, the drug dog comes in, and he's barely better than a coin flip--60% correct. Out of 100 people stopped, he'll correctly identify 24 of the 40 carrying drugs, and incorrectly flag 24 of the 60 not carrying drugs. But overall the process will be right 50% of the time, versus only a 10% probability if you stopped drivers at random. That's probable cause.