Susuto

I’m an extreme grammar nazi and I’m sorry, but I have to inform you that you’re wrong here. In a different case, such as “sisters-in-law,” you’d be right; however, in this situation, if it were said the way you say it, it would mean you made two holes in a single shot. The phrase “hole-in-one” refers to a single shot and a single hole-out, therefore if you pluralize either, you’ve changed the meaning of the whole phrase… ergo you must pluralize outside the phrase itself: “He got a hole-in-one twice in a single round.”