notes for Importing geometry in zbrush:
exporting from houdini
inside geo node, right click -> save -> filename.obj
importing into zbrush
zbrush -> lightbox -> select obj here
exit draw mode
(select an obj file in lightbox) place it, then immediately hit T to exit draw mode
convert to dynamesh
Geometry -> enable Dynamesh
symmetry/mirror
press x settings: transform -> activate symmetrie