I still have an excess of Naphoeta cinerea, Blaberus, Eublaberus etc. but I don`t feed them to newts. If I did I`d be careful because it`s a really fat diet. Another disadvantage is that they have pretty strong shell. Small nympha could be fed sometimes but I think it`s more suitable diet for reptiles.
I have used Argentinian Cockroach (Blaptica dubia) on large species of anura. But I do not think that they would be very suitable for caudates, as mentioned above they are very fast making them virtually impossible to catch unless hand fed and they are not easily digestible due to the hard shell.
I keep a culture of wood roaches (a local species - I'm not sure of which kind). The Tylototriton shanjing that I have seem to relish them (as they do most foods that I offer). Certain individuals of both T. tailengensis and T. kweichowensis also eat them as well while others do not. Worth mentioning is that I forcep feed all of these animals individually and this particular roach species is soft bodied - at least compared to Madagascan hissers and some of the central and south american species that I have worked with in the past.