CNN reports:
The Supreme Court offered unanimous support for police Wednesday by allowing drug evidence gathered after an arrest that violated state law to be used at trial, an important search-and-seizure case turning on the constitutional limits of "probable cause."
"When officers have probable cause to believe that a person has committed a crime in their presence, the Fourth Amendment permits them to make an arrest, and to search the suspect in order to safeguard evidence and ensure their own safety," Justice Antonin Scalia wrote.
David Lee Moore was stopped by Portsmouth, Virginia, officers five years ago for driving his vehicle on a suspended license. Under state law in such incidents, only a summons is to be issued and the motorist is to be allowed to go. Instead, detectives detained Moore for almost an hour, arrested him, then searched him and found cocaine.
At trial, Moore's lawyers tried to suppress the evidence, but the state judge allowed it, even though the court noted the arrest violated state law. A police detective, asked why the man was arrested, replied, "Just our prerogative."
You're completely misstating the ruling. The decision only holds that if the arrest did not violate the Fourth Amendment (i.e., it only violated state law), then the Fourth Amendment's exclusionary rule does not apply.
If Virginia enacts a "do not arrest" policy, then it must also be the one to enact a state exclusionary rule if police violate it. The (federal) Fourth Amendment has nothing to do with it, and the Court merely reiterated that inoffensive principle.
The question of whether probable cause existed is always subject to judicial review. The Court in no way suggested otherwise.