As of YARPP 3.4.3, there isn't any public documentation for what parameters the functions take, as no public API has really been defined. A lot of infrastructure for allowing different settings to be passed in via the function parameters was completed in YARPP 3.4, so this feature is coming. In particular, custom parameters passed to the functions will be the recommended way of using YARPP's custom post type support, which will also be publicized at the same time.
I'm giving a talk on these topics at the upcoming WordCamp Birmingham, in case that's nearby for you.