No, Voldemort wouldn't even get to the Requirement Room, only if he put the horcrux before he graduated the school. Thats the only reason Voldemort wanted to get the Defense Against Magic Arts teacher position, cause he probably wanted to stash something in Hogwarts. But there's dumbeldore in hogwarts, and many other people, wouldn't it be risky to put it in Hogwarts? What about Filch? I think he knows almost all the rooms and stuff like that. It's very tricky. And I think the detail about the tiara was put just to show that Harry hid his book well, and that so he knew it was his, it's a preety good detail to be put in IMO. Common sense. However I am totally against the idea of the Horcrux being Harry.