The idea of using a high-$ verification tool and a free
PDK is slightly amusing.
The lack of open source verification (DRC, extract, LVS)
tools makes the availability of multiple "free" layout and
schematic design tools almost moot, at least for real work.
Some other verification tools (like Silvaco Guardian) will
"digest" Caliber error reports, although that one will not
execute a Caliber deck. You might see what tools are
available to you (how are you doing layout now?) and
whether they include Caliber compatibility in any aspect.
Or have their own rules sets available for your FreePDK.
For that matter you might look again at what NCSU's
real preferred platform(s) are and whether there's one
that is (1) free and (2) can do DRC on a GDS-II database
(since that may be the only medium that you can exchange
layout data tool-tool, by).