Well its your choice of course, but I see nothing that says Blizzard has made thier graphics files public domain. Sure they encourage people to build custom UIs for WoW and use thier graphics, but thats for thier own game. I'm fairly certain Blizzard doesn't want people using thier graphics to get people to play a competing game
As for the UI you referenced in EQ, I already knew about it -- and he did not use any original Blizzard graphics in his UI. Many were handmade, others were at least modified by hand to be different. To "simulate" the look of WoW as he put it.
I don't want to get into an argument about it, I just think you are better off making your own graphics that look as close as you can do, rather than simply ripping thier graphics. You could end up getting yourself, and possibly even eq2interface, into a lot of trouble if Blizzard gets mad.