That's news to me. I haven't spent a ton of time around shadowfiends, but in my experience, shaman and mage elementals and other "uncontrollable" pets (that's why they're called guardians) tend to go after anything that happens to be close to them. That's why they don't get popped when there's sheep or shackles around-- my guild could have used that fire elemental DPS on Moroes, but because it was so important to keep those shackles up, I've been saving the elemental for later. If there really is an AI (and if it works-- even Neth agrees that may not be the case at this point, though she says the shadowfiends on the PTR are supposed to be doing things right), then maybe we can start trusting summoned guardians not to touch CC'd targets until it's OK to do so.
Of course, there's other ways around it-- normally, I just don't pop my pets out until I'm sure there's no more CC left to break, but my pets are leashed to my totem, so with careful positioning, I can still avoid CC. And I believe both mage and druid guardians are targeted-- they open fire on whatever you've got targeted at the time, right? But I'd love a little AI, or at least a little control, in something like my Searing Totem. If there's a CC'd target out there, it's not worth the trouble to drop it even for the extra DPS.