If point guards come up and guard him, he doesn't do it (because they'd steal it). He only tries it when there's not a defender present. So, that's pretty much all reward and zero risk.
From my memory, I can't recall a time when the ball was actually stolen from him. In the Orlando series, if I remember correctly, it was almost stolen, but Rondo recovered it or stole it back right away and threw a pass to Ray from his knees. There have been times where the other team has stolen the inbounds pass, but strictly speaking those weren't times when he let the ball bounce; that's just a bad pass or miscommunication.
Just not seeing the risk v. reward dichotomy here. Lots of reward, and a statistically insignificant amount of risk. The risk, if there is any, is designed, as Doc points out, to get the defender out of position, which actually makes the risk a reward too 
I'm puzzled how you can acknowledge Alston temporarily stealing the ball from him, while at the same time saying that he doesn't do it when the ball can be stolen, and further saying that there's no risk.
There's a definite element of cat and mouse in this scenario, but that doesn't change the fundamental character of the cat or the mouse.
The thing is, part of the play is designed to save valuable seconds, and part of the play is designed as an enticement (and one must court a certain amount of risk to entice). In short, Rondo only does it when the defender's not pressing him, but then he'll usually push it a bit to entice the defender to gamble and press him, so as to gain another advantage over his defender. It's a two-pronged attack--one prong always works (the clock-saving feature) and the other has a variable success rate. This is why it's a smart play--it has guaranteed success. The 'risk' component is manufactured risk (and ultimately under Rondo's control) designed to increase the reward.
Of course there's risk. Alston stole the ball from him, and luckily, Rondo stole it back. However, *of course* there's risk, and *of course* there's a chance of the ball being stolen, because it in fact has happened at least once.
Sure, technically there's risk, but that's why I characterized it as a statistically insignificant risk; it's a manufactured risk (under Rondo's ultimate control) that feeds into greater reward and thus is fundamentally different than the kind of risk associated in the normal risk v reward scenario.
Going back to the cat-and-mouse analogy--there's risk and reward in that scenario, but it's not a risk v reward situation. The cat has all the control, just like Rondo, and gets all the reward, be that reward the thrill of the chase, or the meat of the mouse.