Yes, like nuk3zord7 said, far more often than not. The other nice thing about Rip is that after you successfully pull off a Shred OR Rip on any target that has been Searing Pain'd, you get something called a Lightning Link buff, which greatly increases the chance for your next lightning strike/flash to unbalance your target. This lets you restart your rotation pretty much instantly. If you didn't have Rip, the guaranteed knockdown>OW>SP would most likely fade by the time your Shred cooldown was finally up, which means you'd have to try and proc knockdown manually again-- slowing you down and decreasing your DPS.
That's another reason why I prefer Lightning Flash R3 to Mangle R3. Lightning Flash R3 gives a 100% chance for knockdown to proc after Lightning Link, as opposed to the 70% KD chance of Lightning Strike R3. With Flash, if my pet doesn't miss with its attacks, I can easily keep up a continuous Shred/Rip rotation until my pet runs out of energy.
Btw, with all 3 Battle Training rubies, the CD on Shred would be 10.5 not 7 seconds. With both Shred and Rip, I find that I don't really need the CD rubies at all (I wouldn't ever take more than one, anyway).