You can also import topology from outside zbrush… 
I don’t remember the thread but the process is:
1.- Open your High-Res Mesh, rename it HIRES (Only for reference)
2.- Select a primitive, import your retopology mesh, rename it LOWRES (Only for reference)
3.- Append LOWRES to HIRES, and be sure to be working on the HIRES subtool
4.- Select a Zsphere, rename it RETOPO
Go to the tool pallete > Rigging subpallete > press Select Topology (Select the HIRES tool)
5.- Select your HIRES/LOWRES tool, work with the LOWRES subtool
Go to the tool pallete > Topology subpallete > select topology (Select the LOWRES tool)
Now you can project your topology, the imported topology should have uv’s done…
Another option
1.- Open your High-Res Mesh, rename it HIRES (Only for reference)
2.- Select a primitive, import your retopology mesh, rename it LOWRES (Only for reference)
3.- Append LOWRES to HIRES, and be sure to be working on the LOWRES subtool, divide it some levels.
4.- In the tool pallete > Subtool pallete, hit “Project all” button to project the geometry.