I didn't know a damn thing about the gallery, but I was able to look it up on Wikipedia. From what I can tell, it's a big, basic, commercial gallery that prides itself on its white walls that hold the art. Hence the name, "White Cube."
So, I looked up the two sites, www.whitecube.com and @whitecu_be's site, www.whitecu.be:
They are similar, if you count white backgrounds, sans-serif fonts and a bit of art thrown up on the wall as similar. whitecu.be has more content, and seems to be a better site than whitecube.com, but it didn't take much checking to be pretty sure that www.whitecube.com is the legit site for the London gallery. It's been registered since the dawn of time, all the contact info goes to the two galleries, and it's boring as hell (tedium and dull spaces would be hell for me).
www.whitcube.com may be legit, but it's a terrible site. It has more than one broken image, which for a visual arts company is just plain wrong, and the art they actually display is so small I thought the big images were thumbnails. Oh, and the 7 pt. body font... Good thing I was using Opera and could zoom the entire page.
But then there's @whitecu_be's site, www.whitecu.be which has way more intersting stuff. They say they this about themsevles:
Whitecu.be is a portfolio service for artists and art galleries with unique hyperlink sharing at play. It's simple to use: upload work, arrange the order and pick a layout. No tedious messing around w/ code or other internet bullshit. Get yr internet presence up so you can get back to work!
whitecu.be isn't really pretending to be the gallery, although they're obviously leveraging White Cube's "brand." But I have to put "brand" in quotes because White Cube isn't doing anything with their web presence. Meanwhile, @whitecu_be has over 10,000 followers, a website that actually has interesting stuff on it, and, heck, if they actually have a CMS tool that works, they've got something more useful to the world than www.whitecube.com
Again, I don't know anything about the gallery, but I know their website sucks, so if whitecu.be can run with it, more power to them.