srcare
I'm not sure if this will fix your issue, and I know it's a bit of a late reply, but I was able to get motion blur in c4d/octane (using Houdini exported alembics) by adding a Octane object tag to each object--it won't work on a null-- and then turning on the transform/vertex option. Then turn motion blur on in your octane camera and set your frame rate. Like for 24 fps it would be 1/48. You can mess with the cache to get different results. I only just figured this out myself, but so far found that exaggerating the look gave me the best renders.
Hi I'm also struggling with getting motion blur on a imported alembic in C4D, it used to work with vertex speed but this makes octane crash now. Never got transform/vertex to work... could you maybe share a file or screenshot of your alembic node set up?
Thanks!