sbomnix writes purl (package URL) and cpe fields in the sbom, see the baseline SBOM in nixos-vex: https://github.com/datosh/nixos-vex/blob/6c6bbba6d30cf474dcf...
The nix purls are not supported by anything, as far as I can tell :/ But grype does a good job matching the CPE data!
Grype does warn about some unknown CPEs, for nix build artifacts:
[0000] WARN invalid CPE: cpe:2.3:a:nixos-system-desktop-26.11.20261001.c59305b:nixos-system-desktop-26.11.20261001.c59305b::*:*:*:*:*:*:* from=syft
Do try the demo: https://github.com/datosh/nixos-vex/tree/main/demo/desktop
It should show you what's working today, there are definitely areas to contribute to the respective projects!