Well, I hope I can answer your question quite well. Step by step, let's go:
1st- Are these Rhyperiors hacks? Yes. Since Rhyhorn evolves at Lv.42, the minimum level to have Rhyperior is 42.
2nd- How do these dudes make Rhyperiors Lv. 1 to 10? There are two methods: both use a 3rd party device whose name I am not going to say here due to Forum rules. I witnessed the process myself. It is pretty broken. And the Pokémon Online System doesn't detect it. And it won't so soon, but I hope this changes.
3rd- How do the methods work? One is hatching a hacked egg with an already evolved Rhyperior. But since a Rhyperior can't be hatched from an egg, it can't be traded or used online, the game says "There is a problem with your pokémon." when you try to wonder trade it or deposit it in GTS or Link Trade online. If you link trade it offline via Quick Link, the game doesn't say a single thing about it. The second method is getting a Rhyperior from GTS trading the normal way. Then, using this device, the dude changes Rhyperior's total experience to be 1 xp, so the Rhyperior he got from GTS will be Lv.1. Bingo! And since the original Rhyperior was traded, it won't be considered illegal AND can be used online. Then the dude uses the device to clone it and spam it through the whole GTS.
4th- The same dude can choose if it's shiny or not, adjust EVs, IVs, if it is shiny, its nature, its movepool and whatever you can imagine. Except its name.
The dude who showed me this is not my boyfriend anymore. That's not honest and I dumped him. It's just a game, but if you do it in a game, imagine what will you do in real life. : /
I hope I could answer all your doubts and sorry for English mistakes. I am Brazilian. xoxo ;-)