Yes some will readily take fruit flies, the flies tend to form small floating groups and then the newts come and grab them like some giant shark eating seabirds from the water surface. Fewer flies escape then you would think.
If you've got a couple of floating plants (especially Pistia sp.) some newts will hang on to them to stay close to the surface as the flies use the plants to walk on. When I've caught a annoying house fly or mosquito I feed it to my newts larvae using tweezers.