Does OSX support (importing) OpenVPN profiles? Is there some way to import the settings of an OpenVPN client into the built-in VPN client in Mountain Lion? Or am I comparing apples to oranges?
No.
As of Sept 2012 (and Mountain Lion), macOS does not support OpenVPN in the built-in &quot;Network Manager&quot;.
Out-of-the-box macOS only supports:

L2TP over IPSec
PPTP (not recommended)
Cisco IPSec

However, you can use the following third-party OpenVPN clients in macOS:

Shimo
Viscosity
Tunnelblick (open source, free)
pritunl client (open source, free)

I can confirm that both Shimo and Viscosity support the import of .ovpnprofiles.