As far as I know the Eclipse Che GWT client is replaced by Eclipe Theia in the upcoming version 7 which is currently in beta. But I think both will still be independent projects.
Yes, it is an independent project used by different products like Gitpod (www.gitpod.io), Google Cloud Shell, ARM Mbed Studio (https://os.mbed.com/studio/) and so on. Eclipse Che is going to replace own GWT based IDE with Theia in version 7 as you mentioned.