Using PDs has pretty much become standard in the IDP world. There were wide variations in how the stadium stat crews awarded the stat in its earlier years, but the NFL has better standardized how the crews award PDs in the past two seasons. As unofficial defensive stats go, it's now pretty solid.
As Larry said, corners with ball skills or safeties/linebackers that put them around the ball often in coverage get small bumps in value, depending on how much your system values PDs. If you weight a PD as much as a solo tackle, quite a few corners often move up into your top 25 in the year end rankings.