Yep. If you are talking about the first foot to protect bark from rodents you might be OK, but I would not use them for tree tubes. Tree tubes can have both positive effects on seedlings. They are designed to have proper air flow, light transmission, heat reflection, etc. If not properly designed, you can trap too much heat, create a chimney effect and dry out the tree, retain too much moisture and encourage mold and other disease, and probably even more things. Even with well designed commercial tubes, things can go wrong.
If by tree protectors, you mean for protecting already established trees from rubbing where the tree is growing well above the tube, I would expect you would have less problems. Even for this purpose, I'd check the trees every now and then for the first year or two to make sure you are not having ill effects.
Thanks,
Jack