So...
A Void can Cut a Solid.
A Void can be Joined with other Voids by simply creating multiple Voids.
A Solid can be Joined with other Solids.
But...
A Void can not Cut another Void.
This means Void Geometry is, in the end, more limited than solid geometry.
Example:
I am creating a face-based family that is a void to cut reveals out of other geometry. The family is linear, and has a complex profile. When trying to build a miter angle into the ends, it seems it cannot be done.

Best,
Nick