It seems that some AOV's can not be used properly when a VDB grid object is in the scene. If there is pixel coverage of a VDB object, I would expect that coverage to hold out what ever data is behind it. As it is currently, I can not use a number of AOV's in comp because it is not being evaluated in those AOV's.
For example, I can't use an RGB mask to isolate other objects behind the VDB grid. Other AOV's I would expect the VDB grid to hold out is in source elements and texmap elements. There are more as well, though I'm not sure how they would be rendered correctly (zdepth, UVW, position, etc.).
In the attached example, there is a VDB grid of rocket smoke in the middle of the image in the beauty pass, but there is no evidence of it in the attached AOV's.