I'm uncomfortable with a random man taking over my female roommate's room (sublet) for the summer.
Why do you think that a man would take over that room in the first place?
She's going out of town for a month and subletting the room to some guy while she's away.
It's okay to not want someone else in your space. Especially if you're still paying rent during the summer as well.
She didn't even ask if it was okay with me before making arrangements with this man. I am the roommate after all so I feel like it is my business too.
She shouldn't be able to do that without talking to her roommates.