No matter what you do it's still illegal as long as you use anything that Gravity made. Including their client, sprites, BGM's, server software, skill names, and bunch of other stuff. Every single eA server out there is illegal as well, though mostly with names and client, while aRO uses an actual stolen copy of the official server software. If you'd use eA, change skill/class/other names. Along wtih make customized sprites and maps using your own models then the whole thing would be legal.
But yeah, as DeePee said; Gravity stopped caring. There are thousands of pservers out there, and it'll take way too much resources for Gravity to bring down even few of the bigger ones. So they just ignore em and focus on updating their own servers with content that'll be better than on pservers.
