Plenty of non-gov organisations use various bits of it, for example the breadcrumbs and accordion on [1]
[0] https://www.gov.uk/service-manual/design/making-your-service...
[1] https://www.rnib.org.uk/living-with-sight-loss/assistive-aid...
Edit: Re naming - GOV.UK [Thing] is an established convention for community tools, as shown on [3]. GDS are aware of the project.
[3] https://design-system.service.gov.uk/community/resources-and...