My second question and more importantly, does Vnish use the same CGMiner API format that stock Antminer firmware and several other third-party firmwares use?
For the most part, yes it does tho they've added switches for their code.
Along that line, Vnish violates the cgminer open-source GPL. Vnish is a hacked version of cgminer. They hacked the code and made their version of it closed source.