I don't know if this is the reply you want, but I render almost everything in blender.
It's pretty painful to get your geo into blender, but not as painful as watching mantra render refraction

For most geo you can use an obj with a mdd cache
For changing topology you can alembic to max and then use this tool to go to blender
http://blenderartists.org/forum/showthread.php?390636-Addon-Blembic-Mesh-Cache-that-supports-varying-vertex-count [
blenderartists.org]
We are working on a houdini exporter for this tool, but it's not done yet.
Cameras we alembic to maya, and DAE them to blender.
Sometime you need to rotate the camera, or objects 90 in x, but it works.
We are also working on a houdini solution for this
We are also trying to get vdb from houdini to blender, but this is still a bit of a problem.
This workflow has saved me on a few projects.
Once we have a working tool, we will post it on these forums, but untill then, you can get most of your renders done with the workflow described above.
Like I said, not the answer you were looking for, but it does work.
G