I've used seafoam as a combustion chamber cleaner, IE pour it down the carb while the engine's running to clean out the carbon deposits. I've also used it in the fuel tank of my boat. I'm not a firm believer in putting anything special in the oil, because a well maintained engine with regular oil changes will stay very clean inside. My stock unopened 76 440 was super clean inside when I cracked it open for the first time.

The seafoam is a cleaner, however I don't think one small bottle of seafoam in the oil will hurt anything if run in there long-term.