The audio for all of the voices produced from public data sets is licensed as Creative Commons Attribution Share Alike 4.0 International. This is what a lot of the original data is licensed as.

Full license text here: https://github.com/MycroftAI/mimic3-voices/blob/master/LICEN...

and an explainer on what the legal mumbo jumbo means here: https://creativecommons.org/licenses/by-sa/4.0/