Alucard wasn't playable in POR, though.
In DoS, he was only playable in Julius Mode, and is unlocked simply by encountering him in the castle (I forget where, but you can't miss him since I think you have to go through the area he's at anyway). From there you just push a button to switch from Julius or Yoko to Alucard.
As for the hack, it's actually pretty intriguing. I'd love to replay the main DoS as Alucard, and might even give the hack a go if you were to release it. I don't know if I'd finish it, since seals are a pain with the mouse, but I'd at least get some decent fun out of it.