To my knowledge, since the character is in the public domain, I think it's permitted. You should properly attribute the character (such as providing links and other information) so OGA moderators can verify that you have the rights to use the character.
For clarity, by non-OGA, you mean a character that did not originate from OpenGameArt? And if you may, what is this character?
You're welcome! Yeah, you should be fine uploading sprites of LinuxFox onto OGA.
(Edit) Also, thanks for comment on my PFP.
To my knowledge, since the character is in the public domain, I think it's permitted. You should properly attribute the character (such as providing links and other information) so OGA moderators can verify that you have the rights to use the character.
For clarity, by non-OGA, you mean a character that did not originate from OpenGameArt? And if you may, what is this character?