Is it safe to store unopened metal cans in the refrigerator?
There's nothing wrong with storing unopened metal cans in the refrigerator. But it's pointless in terms of food safety - the whole point of canning is to make the food safe to store at room temperature. Don't waste the fridge space unless you're actually trying to chill the contents of the cans.

Now, if the cans are open, sure, that's a problem. You should transfer the food to a sealed container for storage, whether it came from a can or a pot or anywhere else.

But none of this has anything to do with acidity. Acidity doesn't make you sick, and in fact, it can help keep bacteria from growing and keep food safer. That's why a lot of canned goods have a bit of acid added, and why we pickle foods.