Yes you should tong feed the nightcrawlers because they will hide in the substrate forever if you let them. Try and feed the nightcrawlers so when your frog lunges he gets the nightcrawler on the first try. Frogs are basically far sighted. Your frog can't really see anything up close to his nose, so he relies on his sense of smell and touch to catch the prey if it's close to him. I've found just dropping the worms in front of him to be effective, because the worm graces him when it drops down and triggers his mouth to open and then he gets a feel for where the worm is and gets it. This is easier then holding the worm for him horizontally because the worms will sometimes droop and frog will take forever to take the worm, or sometimes they will lunge and get nothing but steel, but it sometimes works. You will have to learn how your frog reacts and might take you some time to get the feeding just right.

Usually when they want to eat they will come up to the surface. I don't pick mine up from the dirt and feed him or put him in a container to feed him because I think it causes too much stress. Also when they go completely under, they come back up even fatter and usually they sleep during that time and get some much needed rest.