I would disagree. They said things like a flea (at least without blood around) was a big nothing. Never had problems getting in or out, I doubt an absence of mind would be overwhelming. Besides, when do they ever get really caught up in a mind for more than the first few minutes (spare emotional crisises)
There are various suggestions that morphing wouldn't work on plants, but think it's the ultimate KASU that the only requisite we were told of was DNA, yet it seems implied that plants can't be done
But even if you could, why: can't see much more than light/no light, probably can't detect spoken words, can't fight, and if they find you out (via Helmacron tech or the like), they run you through the woodchipper, put you in the fire, no way out but to demorph and be helpless. What can a tree do against a Hork-Bajir?