Something has just occurred to me. In the Edolas arc, there were only three groups of people who weren't sucked through Anima: the Exceed, Celestial Spirits, and the Dragon Slayers. Mystogan survived because he was out of range. Everything else was just gone.
We know Anima absorbs magic, but why not them? Was that ever answered in black-and-white, which is how Hiro likes to give definitive answers? This made me think: could it be that Anima has no effect on living creatures that aren't human? And if so, could this mean that Anima didn't affect the Dragon Slayers because the dragons became one with their bodies?
That sounds awfully similar to the idea that the dragons were what kept Natsu and Gajeel from crossing the barrier that said, "those over 80 cannot cross". There are people who scoff and say it's clearly because they were sent through time, but looking at the other evidence being shown at the time (Igneel and Grandeeney knowing where Natsu and Wendy were, villains seeing images of the dragons), the dragon angle just makes more sense, at least in terms of what Hiro was likely intending at the time.