In as much as one can without it going to actual brother fucking, definitely. He said time and time again that the boys and their relationship was the heart of the show, the very core of everything. That the show was the epic love story of sam and dean. He wrote a show about two boys who lived in each other’s pockets and loved each other so much that their love alone saved the entire planet. He started off writing a show about monsters, originally wanting to make a show that was a horror movie a week, but he fell in love with his own characters. He loved jared and jensen’s chemistry and got so wrapped up in the boys he created that them and their relationship became the entire show. And he went as far as to make episodes that actually broke the fourth wall and talked about wincest, tossed in an actual wincest fanfic and shipping cosplayers.
No one but him could say if he actually digs slash shipping or not [I wouldn’t bet on it], but in the sense that he loves sam and dean’s love? Very, very much so. I mean, just -