While playing Vlad today, I noticed "Tides of Blood" doesn't proc spell vamp. The ability does magic damage; why doesn't it absorb health?
Edit: I was playing a bot game with around 600 AP, a Spirit Visage, and a Will of the Ancients. I used Tides of Blood while surrounded by 10+ minions and noticed no spell vamp. Magic dmg should have been ~450 to each minion, so 450 * (.25*.33) = ~37, not counting spirit visage.
It's possible I just didn't do enough damage to trigger the floating text, but I started watching my health bar to see. It's difficult to tell since Tides of Blood damages Vlad when cast, but I still should have been gaining 300+ health.
It was late when I posted this, and I must have made a mistake. I was able to confirm last night that Tides of Blood does proc spell vamp.
Side note, I often noticed only 1 green number pop when I got high enough. It seems they've combined the floating text into one number, making it easier to see how much health he gets back!