Why ask a question you already answered previously in the same post?
Of course it is not a real place... Star Wars is *gasp!* not real!
Anyway http://starwars.wikia.com/wiki/Hook_Nebula took 2 seconds to look up. Okay maybe 3, but still it took you longer to write that question than it did for me to search.
Do you know what a nebula is? In theory it should be a very gassy place (not the crystal clear background for the system that it shows) and those stars there would likely be a lot smaller size and still growing. Those 6 would eventually likely fling each other out amongst the rest of the galaxy. but for now, in its infancy, they are together and I guess the admins decided not to include a "canon" planet in the system, not sure why.
I believe there was already a system that was purely suns coming from the galaxy update - so its not the only one. I'm sure tyere is a way to balance the gravity between them so they all have stable orbits.
There's a puppet master beyond me, who may or may not have formed the nebula. As per why there was no planet there/Santarine was not, is the fact Hook Nebula is the name of the system as well as the sector, with the Santarine planet being in it's own system canonly.
As to why the nebula was added on its own, I'm more than content with there being obscurities within our galaxy.