Arguably, R and G are half-men because they both serve the exact same purpose in the "Hamlet." Not only that, but they are completely interchangable as characters - it doesn't matter which one is R and which one is G - they are pretty much the same person. Even their dialogue is interchangable, and the way other characters treat them. Many productions use this to a comedic effect, especially in scenes such as the one in which Queen Gertrude welcomes them, stating G's name first, then R's, followed by the King, who greets them the same way but just switches the order of their names. A lot of directors like to "play up" such moments in "Hamlet" by making it seem as though no one rally distinguishes (or is able to distinguish) between the two men.
Tom Stoppard even chose these two men as the main characters of his play, "Rosencrantz and Guildenstern are Dead," in which their identity is still arguably interchangable and he pushes this idea to existential heights.