I'd be shocked if it's anything other than Dwarf Golden Arborvitae (Thuja orientalis 'Aurea Nana'). Most of the bonsai I've seen out of these were uninteresting mallsai types. I've seen a handful of larger ones made into credible bonsai, including a couple of dramatic windswept bonsai, but I'm told by those who own them that they are hard to maintain their shape.
Cheryl Manning did a web page about what she did with a similar hedge.
http://betterbonsai.com/treasure/hedge/hedge.html
This may be a temporary glitch, but when you click the link, you have to delete the www and hit enter again or you'll get a "server down" error.