AMD announced at the XDC2015 Toronto conference that it's working on a Vulkan driver for Linux. The firm has a prototype driver ready, initially this will be released as a closed-source driver but AMD promises to open-source it at a later point.
This was the first time we've heard AMD's Linux team talk about Vulkan... They are working on a Vulkan Linux driver and have one prototyped, but initially it will be closed-source and the open-sourced later... They also mention that OpenCL support will initially be closed up and then opened later. They already have some basic OpenCL open-source support via the Clover Gallium3D driver, but I imagine they're referring to OpenCL 2.1+ support with SPIR-V alongside Vulkan or the OpenCL Catalyst code.