Man pages are their own thing -- although the end result could be the same with some aesthetic differences (man pages does not support colors per-se, though with a config you could style your titles or emphasis).
rst2ansi is a more generic document renderer, that may be used in another program to render document parts. It doesn't convert the document to an intermediate man page, nor specifically formats the document as, well, documentation.
The closest thing I think of given your example is how the --help flag in git displays the manpage instead of an option summary. Is that the sort of thing you have in mind?
I originally made this for an interactive index where you can query some document parts, and these parts are written in rst -- in essence, it's almost the same: rendering an arbitrary document into a string, that you may or may not manipulate later.
rst2ansi is a more generic document renderer, that may be used in another program to render document parts. It doesn't convert the document to an intermediate man page, nor specifically formats the document as, well, documentation.