A new update to V-Ray 3.0 for Maya Beta is now available. You may now define render regions using an object selection or image mask using the Render Mask feature.
If you’re participating in the public beta, be sure to download this latest version.
• Render Mask support
• Support for Maya 2015 (OSX)
• Simplified render settings user interface
• VRayFastSSS2/VRaySkinMtl: Optimized raytraced multiple scattering
• Optimized rendering performance with tiled textures
• Optimized primary visibility with Maya Hair and V-Ray Proxies
• Reduced memory usage for hair and particles
For more information, check out the the full feature list for this update.