It's perjury if the term "confidential source" legally implies it was information conveyed by a human informant instead of gathered by electronic surveillance. The definitions I can find online say that "confidential source" is synonymous with "human informant" and must be a person. While this might be a "legal person" which includes a corporation, it would be a stretch to call a Stringray a person.

In my mind, they are simply lying about an illegal wiretap, and "this has not been challenged" only because the lie was taken as truth. But I'd guess the exact phrase was well-crafted by a lawyer who thought this alternate "plain English" interpretation would work as a defense. I'm doubtful a judge would view this charitably, but as you say, a prosecution where we find this out seems unlikely.

Is it evidence? Sounds like they're using it to locate people who are already wanted by law enforcement, not to gather evidence of a crime. What's the recourse there?

To me, although not a lawyer, doesn't matter. This is just my gut instinct of what is right.

If a person is a defendant then that person has the right to face all the evidence being used against them. If the defendant feels that a certain part of evidence gathering was done illegally then they have the ability to question that gathering in court, of which the court will decide the legality of the gathering method. If the prosecution has the ability to conceal methods of evidence gathering then that means the defendant has no recourse.

If a person is under investigation, the police use a method to locate and/or track the suspect, and that method ultimately leads to an arrest because of where they happen to be while being located and/or tracked then I feel it should be included as evidence.

But I'm not familiar with court cases concerning such technology so it's possible that all this has already been decided and I just haven't heard of it.