the ingredients for the pellets include:
Ingredients:
White fish meal, shrimp meal, alfalfa meal, wheat flour, alpha starch, brewer's dried yeast, l-lysin, dl-methionine, fish oil, vitamin A supplement, l-ascorbyl-2-polyphosphate (source of vitamin C), d-activated animal sterol (source of vitamin D3), vitamin E supplement, thiamine mononitrate, riboflavin, choline chloride, inositol, calcium iodate, manganese sulfate, magnesium carbonate.
Nothing there has copper in it so you don't have to worry about that. Some Hikari foods do have trace copper in them, but I don't see trace as a real problem. Many ornamental shrimp foods contain trace copper and shrimp are as sensitive as axolotls.
Most animals need some trace minerals and metals that are toxic in larger than recommended doses. Afterall, trace copper is needed for red blood cell formation, connective tissue, and to help store and release iron to help with hemoglobin... and it helps with brain function. So while toxic in larger doses for axies, it isn't bad in trace amounts. Note I am saying trace here.
I've fed carnivore pellets to a number of larger fish over the years and they are a nice pellet. Good quality and it doesn't usually take an animal long to get onto them. I can't see why they wouldn't be good for axolotls.