Can we use 0patch in parallel to Windows Extended Security Updates?

Yes you can. Obviously our post-EOS Windows Server 2012 or Windows Server 2008 R2 micropatches won't be applied (or needed) on a computer with ESUs installed, but our micropatches for other software products will still get applied. In addition, should we issue a micropatch for a published 0day on Windows Server 2012 or Server 2008 R2 before an official fix is available from Microsoft, we will make one for both fully updated Windows systems without ESUs and Windows with ESUs installed.