Supposedly this particular private server is pretty legit. They require that you have a legit copy of the game with a legit CD key. Supposedly their server software was developed without using any of the code from the original game or server. Whether or not this is true I don't know but the site has been up for a few months now and I haven't heard any news of Sony Online Entertainment sending legal notices their way.
It is legit -- I've played it many times, though not recently. You have to own a copy of the game to play it and you install a special launcher they created which will load the proper files (I think it is at patch level 13, IIRC) and connect to their server. FYI, the site has been up for years, not months.
The server software was completely engineered from scratch and has gone through a few major revisions over the years. At this point, they are rebuilding the object models (called the Object Restructuring project) to better organize the code to allow future expansion and growth. Furthermore, there are teams of people already working on expansion material for the game.
Will it ever come to fruition? Hard telling at this stage, as it is taking forever. The EMU is fun and has most (but not all) of the core mechanics in, and it is complete enough that you can master many (most?) of the master professions. I loved the old game and hope it does work out, as I need a good MMO to play.
A couple of years ago, the EMU team did meet with both SOE and LucasArts about the project. They would never publicly reveal what went on in those conversations, and rumors were all over the place including one that said that LucasArts wanted to host servers when the code was done. Take that with a boulder of salt!