If Danny was able to document his results and process and store the evidence properly then it likely would stand up in court.
A defence attourney would argue that the tests weren't accurate enough, that's their job. But if Danny could prove that what he'd done gave an accurate result (and no, I can't remember what he did exactly), then it'd be okay.
The biggest difference with Cath was there was no chain of custody going on. No way to prove that the samples she was bringing in were from the crime scene i.e. her. A defence lawyer could have argued that there was no way to know just when and where the evidence had been obtained. Danny wouldn't have had that problem.
At least that would have been my reading of it.