Is it there a flash player for the GP2X? Yes. I have no idea how well they work, though.
http://wiki.gp2x.org/wiki/Pocket_Flash_GP2X
http://wiki.gp2x.org/wiki/FlashPlay
Now, it should, in theory, be possible to port Gnash, the GNU flash player, to the GP2X, but I've got no idea who would do...