Hornworms are good feeders, so i wouldn't say neglect feeding them out of fear, but like others have said, maybe put them in a plastic cup or something they won't grip well. It just looks like their grip on a branch could hurt a chams tongue to me. I Wanted to see what others thought...EVerytime i see something like this i think of one of the horror stories of "my chams tongue just fell off"
on a side note, I find that when my cham is well hydrated, his tongue is much less sticky and seems to be better at shooting at things and not sticking--I've only ever had problems when he was dehydrated--although this doesn't apply to the hornworm scenario where the worm is just gripping hard.