I have substrate based planted tank with soil underneath the gravel. When I feed blackworms, I put them in a submerged shallow plastic or glass dish. I use a plastic petri dish or the lid of a glass butter dish. I it doesn't sink by itself, you can weigh it down with a small rock inside. I aways leave a small unplanted patch for that purpose in the front of the tank.
The newts quickly learn to grab the worms out of the dish. A few worms will escape into the substrate, but that isn't a problem. The newts will hunt tose down at other times. The worms will stick their ends out of the substrate at night and that's when the newts can get them.
In my opinion, densely planted tanks are the best and easiest to maintain and have the most reliable water quality.
See pic below