I had a plec kill an angel once, but i was completely my fault.
Under normal circumstances plecs and angels are a great combo. Kept them for eight years and no normal problems.
But unfortunately...
I fell asleep during a water change and unintentionally drained the tank down to less than an inch of water. The plec found an angel, necessarily laying on its side, and started rasping on him.
Black Angel male five years old and half of a breeding pair gone in a couple of minutes all because I was an idiot. Lowest moment in my fish keeping "career".
So unless you're a dumbass like me it should make a wonderful combo for many years. Good Luck.
Carl