I mean, if we look at the rules for morphing and the way the process works, it doesn't make sense, does it? I mean, you're taking the DNA that you're focusing on, morph it, and your mass or DNA or whatever goes into z-space. So if one was, say, to morph a red-tailed hawk, over stay the two hour morphing limit, and get trapped, it's not a human anymore--save for the intelligence part. So, if we have a new creature, and we know from Animorphs 39: the Hidden that animals can morph, too, then according to the rules it should be able to morph, shouldn't it?
From a plot stand point, it makes sense. I mean, there's not much at stake if Tobias got trapped and they just gave him his morphing powers back. It wouldn't give him his body back, but it would help him get over some of his wangst.
Seriously, though, aside from plot, why can't nothlits touch the morphing cube and regain the power to morph?