No the probable cause would not get thrown out. The dog was trained to alert on drug's. There is no way to train a K-9 as to illegal or non illegal drug's.
More so then that you would only need Reasonable Suspicion about the drug's to go further in an investigation.
BILL
Well, in Washington state anyway, the State Supreme Court has ruled that just because a person is openly carrying a firearm does not justify even a Terry Stop by a police officer to determine if the person is in lawful possession of the firearm or not. Why? The police officer has no indication at the mere sight of a person carrying a gun that the gun is illegally possessed.
So, why would the rules change for a dog alerting on the presence of drugs? Just because the dog alerts is no indication that there are drugs that are illegally possessed. Only that there are drugs present, exactly the same situation as a gun being carried.