If the warrant was valid, and honestly, even if its not - in a circumstance where disallowing the evidence would serve no deterrent effect on law enforcement (rare that it does rofl), then any evidence of a crime, even if it's not the evidence originally sought, is admissible, contingent upon relevance and competence. Competence shouldn't really be an issue in a lot of circumstances, as the evidence should come in as an admission which gets rid of the hearsay concern, and metadata isn't hearsay because it's computer generated (not a person).

The other part of relevance is the evidence's tendency to prove or disprove a material fact - which, assuming we are charging all the cunts involved, this shouldn't be an issue. What may be an issue with some of the evidence, is that it may be so inflammatory (tapes of murdering children), mislead the jury, confuse the issues, probative value outweighed by prejudice, etc. that a judge deems it inadmissible.

I think the big takeaway in all of this is that the info comes from an investigation, and isn't just handed over by the NSA, even if it really was…