While most peaches do not need pollinator companion, most plums do. In the past, the mantra was (and still is) American plums need an American plum companion, European plums need a European plum companion, and Japanese plums need a Japanese plum companion. This is still generally true, although just like sweet cherries, hybridizing and selection has produced some self pollinating varieties. But it would be unlikely that a plum tree grown from seed would be self pollinating.
