This has been known to work, you are right... But you hear of dogs and wolves living in harmony that does not ensure it'll work. I know that's not what you want to hear but I have a few tips that may help if you decide to get them both anyways.
Talk it over with your wife BEFORE you get the kit to make sure that's what she really wants because you will want to get your micro pig FIRST to adapt to your home. Bringing home the pig and bonding with it first will help it feel safe and secure, and much safer than getting them at the same time or bringing the pig home after the kit has claimed your house as it's territory. Animals can sense chemicals produced in the body representing stress and fear, and foxes prey on the weak, plus you don't want your piglet stressed anyways. You want the Fox to be the "bottom of the pack" from the beginning... Keep in mind you may have done a very good job training both pets, but later down the road genetics and instinct can be triggered.
When you bring the kit home you want to have waited until your baby micro pig is at a size that is bigger than the kit (I'm not sure what ages your bringing either home, but size is just as important). If you plan on crate training or litter training them, make sure they each have their own crate and their own litter boxes, separated on two different sides of the house. You want safe space for both animals, space that can be their "own territory". Foxes mark throughout their territory, and if this becomes an issue at least it's more likely to be in a selected and seperated, trained space. If you don't plan on crate training both (although I highly recommend it), you will want to figure a way to separate them when you're not home to keep them safe. Crating is the best option but i suppose you could install a screen door somewhere in your home.
Hope this helps! Good luck either way, foxes and pigs can be difficult to raise if you aren't home much, they both will need ALOT of at attention and one-on-one time. This is especially important for ensuring they behave together and get along, they both must trust you and your wife enough, and look up to you as their leader to mind you.