Chaos Group shared a blog post explaining the possibilities and limitations of USD and Hydra in V-Ray 5 for Maya and Houdini.
USD also known as the Universal Scene Description, a magical interchange format developed by Pixar, came to V-Ray. So now V-Ray can handle all types of 3D and animation data and allow for a faster, more efficient workflow where you can easily take the data to one app, transfer it to another, and import it back into V-Ray. You can find USD support in V-Ray 5 for Maya, update 1 and V-Ray 5 for Houdini, update 1.
Apps can support USD either using a USD procedural or using a Hydra delegate. V-Ray makes it possible to use both methods and considering that Houdini Solaris supports Hydra while Maya is mostly focused on USD, adding those two to V-Ray was crucial.
As for now, however, USD for Maya in V-Ray has a few limitations. It currently supports static, transforming, and deforming meshes; V-Ray shaders and materials in USD; rendering USD edits with V-Ray in-memory, and a few more options. Rendering support for hair and particles and other features will be added later.
Speaking of V-Ray 5 for Houdini, update 1, "most V-Ray features are already integrated natively into Solaris as supplemental V-Ray options where applicable, such as lights, render settings, render geometry settings," the Chaos Group team notes. Environment Fog, V-Ray Proxy, and other custom procedurals are coming in the near future.