Just use it. I only use saturated fats in mine (mostly lard and butter) and I use metal utensiles which helps to keep it smooth. I avoid vegetable oils because I find that they go sticky (they're also not as good for you to cook with as animal fat).
It's not that metal can't scratch it; it's that NON-stick surfaces are highly vulnerable to being scratched by metal, whereas cast iron is much, much less so, and scratches can heal as long as you cook with more oil.
I think what was meant (and that I can anecdotally confirm) is that metal utensils do a much better job of stopping what I will call "gunk film overgrowth" during cooking.
