If you look at how the Yaw derailleur works you can see how ripping the derailleur off, while unlikely, is possible. Normally a front derailleur is lined up with the chain rings so such an action is not possible. Since the yaw derailleur isn't lined up with the chain rings per-say if you trim the front derailleur from big to small, which it's not designed to do, it can present a situation where you could rip it off. Again, it's unlikely and I'm sure there will be lots of people saying theirs works fine, but Sram says it's possible. Besides, are you really going to buy just the 2012 front derailleur and say, "oh, that's good enough, I'll stop there."? No, you're going to get shifters too so it's nothing to cause a big fuss about.
There are lots of things in this world, even outside of the bike world, that "work" even though they're not specifically engineered to work together. Does that mean you should do it? That's ultimately for you to decide.
Since I am using the yaw with older front shifters, I'd say baloney
The trim function is not needed but it only affects down shifts
Other than that, all the shift lever does is move the derailleur and the limit screws control how far up and down it goes
So I can't fathom how it would matter in the least which lever you use