Do people generally model in programs like ZBrush and then import to Houdini or do most just model using Houdini's tools?

Looking at which method would be the best work flow.

Is there any good tutorials for importing models into Houdini?

Thanks,

soulcatch
Do people generally model in programs like ZBrush and then import to Houdini or do most just model using Houdini's tools?

Yes and No it depends really on what you want to do and how!!!

Organic Modeling => other tools (zbrush, 3D Coat, Cinema 4D …. )
Procedural Modeling => Houdini

You also can do organic Modeling in Houdini but you mostly want then to make it procedural to have like a generator.
simple example: https://www.youtube.com/watch?v=2b11iiBjS9Y [youtube.com]

soulcatch
Is there any good tutorials for importing models into Houdini?

you can use the File Sop or under the Menu: File > Import > Geometry / FBX / Alembic build the nodes by this importers

special tutorials for zbrush and houdini this one can help:
https://vimeo.com/22488816 [vimeo.com]

If you are new there a tutorials how to start to use houdini:
https://www.sidefx.com/index.php?option=com_content&task=blogcategory&id=202&Itemid=361 [sidefx.com]