Karen Berger's line wasn't called Vertigo, at the time. That came later. But, Perez's WW was part of her line of books, along with Moore's Swamp Thing, Gaiman's Black Orchid and Sandman, Morrison's Animal Man,, Milligan's Shade, etc. This was back when those books were still part of the main DCU. Batman and Superman both turned up in Swamp Thing and Sandman, for example. JLA villain Dr. Destiny was the villain of Gaiman's first Sandman arc. John Constantine made a guest appearance in Wolfman's and Perez's Teen Titans.
Those titles and characters weren't considered something separate from the rest of DC, back then, though they were obviously more mature than most of the DC line. I understand why they separated them, eventually, but I miss when Swamp Thing or Constantine could just pop up anywhere.