(First: we're aware that the DNC stuff is not well documented. Thanks for being the one to blaze the trail!)
There's a one-time step that converts the DNC data from its original VPF format to our intermediate format called DNC_FLAT. To do the conversion, see the Vpf2FlatExample class. Once you have a DNC_FLAT directory, you can point RenderCacheConfig.flatParentDir at it, and DncPainterExample should work.
The VPF reader expects a directory tree like this:
vpfParentDir/
dnc01/
dnc02/
...
dnc29/
a2950077/
a2950080/
...
h2960050/
cul/
ecr/
hyd/
...
In DNC parlance, each dir at the "dnc01" level is a "database," each dir at the "a2950077" level is a "library," and each dir at the "cul" level is a "coverage."
You don't need to have all the "database" dirs -- you can have a parent-dir containing just "dnc06," or whatever. Vpf2FlatExample will convert whatever databases you have to DNC_FLAT.
However, if all you have are the "cul," "ecr," etc. dirs, I don't know whether that's enough -- there may be necessary index files or something in the "database" and "library" dirs. If you have a way to get an entire "database" folder, that's a safer bet. Otherwise, we can try to figure out how to take what you do have and put it in a dir structure as close as possible to what the VPF reader expects, and see whether that is sufficient.