There are some noted workflows that you can follow that will get you a motion vector pass on ABC, Alembic files. Most will take into account the renderer that you will be using, but CG Virus, posted a novel and cheap approach recently.
A trick for getting cheap Motion Vector Pass for Alembic
Here, he shows a trick for how you can get a vector pass for Alembic files in Your Favorite App. In fact, it is shown over again, in Side Effects Houdini first, Maya, Fusion and finally Nuke. This method is cheaper, i.e. less resources, including system resources, setup and render times.
