I did this with a brisket a couple weeks ago. I thought about buying tallow, but decided to just render the fat from the brisket trimmings in a foil pan on the smoker. I was surprised at how well the paper kept everything contained and felt the brisket was juicier and more flavorful than what I get from my typical foil wrap finish. I’ll surely be doing it again.
I only wrap ribs in foil to rest/hold them and never thought about adding tallow. Not sure I will with pork ribs since I’m always happy with the moisture, tenderness and flavor, but may try with beef ribs since the brisket turned out so good.