As long as they're for personal use and not offered for download publicly, that's fine.
If you plan on offering them to others to use, please let us know and we can figure something out as far as attribution is concerned.
The donate link on our main site can be used to become a donor. http://www.octosharkstudios.com/pvkii/
Be sure to include a link to your steam profile page when submitting your donation so we can add you to the donor group.