I'll admit I'd never heard the term "compersion" but have experienced it. I am one who really enjoys seeing my SO at the "top" of his game. It's amazing to me to watch him when he's with another woman. I LOVE it. Truly love it. We've been together most of our adult lives and made love and have lots of passion. But when I see him with another woman I completely melt. And I've watched and then led to participation and watched and masturbated. All is awesome for me. But I love a woman's body... how can I blame him for feeling the same way? Or better yet, why not enjoy him liking what I like? More in common.
Is it voyeurism? Wiki def is
Voyeurism (from the French voyeur, "one who looks") can take several forms, but its principle characteristic is that the voyeur does not normally relate directly with the subject of their interest, who is often unaware of being observed.
Yeah, what I enjoy isn't the least bit "sneaky." So I'd have to say no.