Yes, some are working on this.
Those are libs built from the ground up, they do not use the SDK, although one has to be careful not using the original SDK's code in any way (see “Legal” in LibVR's README).
You could still work with the Oculus SDK if the license doesn't bother you. It's not compatible with GNU/Linux yet, but adding support should not be too difficult, and the licenses allows you to do this. Furthermore, Linux support is actually planned in a later official Oculus SDK release.