I remember Stevo posting a Rakdos steal/sac deck that looked good because he was playing
Devouring Swarm. He was also running
Scavenger Drake, though, so I could be wrong.
The problem with most decks I've faced, and why I think they're bad, is because they load up on three-mana 1/1s and eight steal effects. It looks good until you realize that your opponent actually gets to interact with you and that your deck is super-slow, dies to removal, and is full of dead draws.
If you're going to steal/sac, you need to present a serious clock or you need to get tricky with Cloudshift.
Scavenger Drake (and its close relative,
Rockslide Elemental) are important to Sac/Steal decks because as you say, you need to diversify outside the main theme. As you're either going to be killing a lot of things yourself, or you're going to have your own enablers killed in order to stop you doing that, you need something that generates value out of all this dying and provides an additional threat.
My build is essentially a Goblin deck in the early game, a Sac/Steal deck in the mid game, and a beatdown deck in the late game (if it lasts that long) You can't
Shock my
Bloodflow Connoisseur if I can eat a
Krenko's Command in response to take it out of range, which is only further growing the Drakes and
Rockslide Elementals as parallel threats, with Steals clearing the path for them for large amounts of damage regardless of whether I can sacrifice the steal or not.
Most people just throw in 8 Sac creatures and 8 Steal effects, then pad out the deck in Rakdos colours without really thinking of how anything else interacts with this core, which is where they fall down. Boros Steal would work to a degree, but you have to realise you now only have 4 cards that combo with steal effects in
Cloudshift, and they not only require additional mana, but can be disrupted by counters or bounce, wheras Sacs cannot be responded to. Cloudshift also has no other use, so will be often a dead card.
Sure, you can also pad out the Cloudshifts with
Blasting Stations and
Flings, but then they make your strategy a lot more inconsistent as they all do very different things to each other, whereas 8/10 straight Sac effects make for more more consistent draws.
I'm not saying the Rakdos version is amazing or anything, far from it - I only run it because I find it fun, but it is a lot more intelligent and reliable than it's given credit for, mainly because most people online make poor additions on top of the 16 card core and then make frequent misplays with that too because they fundamentally don't really understand how or why the rest of the deck should or does work - they just copied the core off someone online because they though it looked cool without even considering how to make the rest of the deck intelligently support it.