Just got this from the MentlRay 1.5 docs

Using mental ray® for Maya® version 1.5 User Notes
Unsupported features

mental ray for Maya does not support the following Maya rendering features:

all postprocessing effects: Paint Effects, shader/light glow, optical effects, 2d motion blur, and fur rendering.
software rendering of particle systems
direct rendering of Maya subdivision surfaces
Interactive Photorealistic Rendering (IPR)
Field Rendering
Pre/Post Render MEL scripts
Fluid Effects