While recordings from a scanner may not be given too much credibility in the courts of law, they can be used as evidence that the transmissions took place and if the FOIA requests (or legal requests for them as part of the "discovery" process) fail to turn them up, they may be used to provide some "reasonable doubt" during the trial. It may be hard to prove their validity and accuracy, but with enough work, it may be possible to get the judge to allow them to be used as evidence. Just be ready for the other side's legal team to not only fight to keep it out of court, but try to show that it wasn't what it appeared to be (not from their agency, from another time, related to another offense, was part of a 'training incident', etc.).
The recording can also be quite useful in the "court of public opinion" if broadcast by the media as part of their coverage of the event or trial. The validity is probably easier to show to the media, especially if the audio makes 'good copy'.