It makes any findings inadmissible.Yes, a court order does make it legal - even if the court order was based on false intelligence.
If a judge orders a warrant to search my home for drugs, and no drugs are found, that does not make the warrant "illegal" - even if they used a false tip as the basis.
No, it doesn't.
The findings would only be inadmissible if another (higher) judge found that the initial warrant was issued in error of law, not error of fact.
In other words, if the initial judge signing the warrant made the legally correct choice using the facts on hand at the time, the warrant is valid and the evidence found is admissable - even if the facts on hand at the time are later proven to be incorrect.