DMM will take great lengths to protect its business, which already includes plenty of objectionable content that will normally be prohibited in the West, from foreign forces, feminists, moralfags who may happen to poke their noses in that site. "Opening up" will spell doom for DMM.
It's possible to sign up for an account even without a Japanese IP (hence the language option that pops up when you visit using a non-Japan IP), you can go around, but you surely won't be able to play games in the netgame area unless you're using something to circumvent the IP block, let alone register to those games - you'll be greeted with an offer to play the same game on Nutaku with a redirect link, just like Nutaku will redirect to DMM if you happen to be Japanese.