The fact that the Stations are designed as those for the Princesses of Heart is not a coincidence. It probably has something to do with Ven, that I can agree on. So in other words, Ven is somehow connected to Sora's Dive to the Heart.
But the Princesses hearts were also in the Dark Keyblade, which, I guess, is how the clue is supposed to tie in. Meaning that because Ven is connected to the Princesses, he has something to do with the Dark Keyblade.
Namine saying "You won't disappear, you'll be whole" yadda yadda... eh. Maybe something to do with Sora striking himself with the dark keyblade earlier, dunno.