The ostree project has a description of how they think ostree is related to nix:
[NixOS] was a very influential project for OSTree. NixOS and OSTree both support the idea of independent “roots” that are bootable.
In NixOS, files in a package are accessed by a path depending on the checksums of package inputs (build dependencies) - see Nix store. However, OSTree uses a commit/deploy model …