I think the example is more like:
1) Person is browsing through an image gallery.
2) See's image of Fillia (or Beowulf or whomever).
3) Does not know who this character is, but likes her/his design.
4) Looks it up, possibly buys and plays Skullgirls.
The idea is not that the derivative media helps exposure BECAUSE its pornographic; it's that ANY derivative media bolsters interest in the original work.