Slow cooked ham hock black eyed peas
Diced ham is a great addition to any dried beans, peas, or lentils, especially for those of us who like a lot of meat in them. I would encourage you to add the diced ham later in the cooking process rather than at the beginning. 

You should get plenty of seasoning from the ham hocks. And while the ham can add additional flavor, you run the risk of "washing out" the taste of the ham. (I learned this the hard way may years ago.) Long cooking doesn't hurt the texture of the ham so much, but it does seriously hurt the flavor. 

Plus, it is possible to over-season or get too much salt in your dish. You don't want to do that either.

Ideally, the ham only needs to be added for enough time to heat it thoroughly and incorporate it into your dish. Your 10 hour idea may work fine, but I would think 4 to 6 hours would be sufficient. Again, you want to avoid losing flavor in the ham.

As a side note, slow cookers vary widely as temperatures go. Be sure to check the temperature of your dish on warm to ensure that it is not in the danger zone for many hours.