I have been working on my Sion AD and have been experimenting with Statikk Shiv in order to farm easier. As the game was coming to an end my CS was high, but it didn't seem to match with the extra health from Enrage.

I didn't take any screen shots, I was wondering if anyone knew if kills with Statikk Shiv generated bonus health with Sions E.

I have no idea with sion or nasus, but I do know it works with gangplanks parley for the bonus gold

For Sion, it doesn't matter HOW he kills something, as long as he kills it. Yes, this means that Smite gives him max health.

Here's how the minion kill stackers work.

Thresh: If a unit dies within 1900 units of him, a soul appears (or has a chance if it's a small minion)
Sion: If he last-hits a unit period, he gains bonus HP
Veigar: If he last-hits a champion period, or last-hits a unit with Baleful Strike, he gains bonus AP
Gangplank: If he last-hits a unit with Parrrley or an effect attached to it, he gains bonus gold
Nasus: If he last-hits a unit that he targets with Siphon Strike, he gains bonus damage