CWM Tether.app vs OpenVPN on Mac OS X / macOS
An "Error loading /tmp/tun.kext" in Clockworkmod's Tether.app for the Mac typically (often?) means that Tether.app failed to detect and unload an interfering tun/tap kext.
Tether.app thus gets an error return from the OS when it tries to insert itself into an already occupied spot.
TunnelBlick client works
CWM Tether.app does OK unloading the kexts for TunnelBlick (and probably Viscosity, though I don't have that). However, the OpenVPN kexts weren't found and turned down by Tether.app as of May 2016.
My Fix: Uninstall OpenVPN client, use TunnelBlick in its place
My solution was to uninstall OpenVPN completely. I only had OpenVPN present to see it fail for data center VLAN access, and had months ago switched to TunnelBlick for production use.
After I completely uninstalled OpenVPN, Tether.app can load its kext, and tethering works for me.