Endless Online uses DirectX, so is unlikely to work. However, I grabbed a copy to try it. If you run the Econfig.exe in wine and turn off all the sound, and make sure it will play in a window, (click save after, then it will crash when you close it - don't worry, the config is already saved) the game will load to the title screen, and you can create accounts, login, create characters, more than I expected wine would manage. But once you get to the game world an assertion fails. I don't know enough about wine to work out what is going on, but if I get some time I might look into it at some point.
Wine isn't really designed for playing games, you might be better looking at Cedega (
http://www.transgaming.com/) This is a pay for service, but if you will use it it is definitely worth it as these guys are doing a great job.
Hope that helps.