If you wet the food first so it is soft you can feed it to your flytraps. They appear to react readily to re-wetted freeze-dried bloodworms. Freeze-dried flies sold as "Anole Food" works great too.
Put a wad of the soft food in the trap and brush the trigger hairs a couple times with a toothpick or needle,
The trick is you have to very gently squeeze the traps several times over the course of an hour or so after they close. This simulates live prey moving within the trap. You want to get type 2 closure where the margins of the trap curl outward and a pocket/pouch forms from the leaves.
That's not true, my outdoor Dionaea and Drosera catch very little or even nothing on their own. My Sarracenia must be more attractive then the flytraps because the tubes are usually full by the end of the growing season.
Several field studies appear to show VFTs in the wild catch more ants and spiders then flying insects. There's very few of either spiders or ants on my balcony.
Besides a little supplemental feeding of seedlings or pullings which are too small to capture the typical house fly doesn't hurt.
And some people just like fooling around with the traps. When the sense of wonder goes out of growing these amazing plants it's time to move on to something else.
I can attest to this, while my pitchers are almost constantly full and they do better than the Flytraps, my Flytraps do rather well. But, their main meals seem to consist of spiders and a couple of ants, I've only seen the rare wasp or actual fly caught in the trap every once in awhile. More often than not, I see daddy long-legs' legs sticking out of the maw. It's quite neat.
As for the question, I do not know. I've never tried feeding them anything other than what they catch on their own. They'll probably be fine for quite awhile without food as long as you provide them with other adequate conditions, feeding isn't a big deal. Unless they're going to be in a food-less environment for the long haul, I think you don't have to worry about it.