We believe you can! With highly customizable NPC behaviors and extensive worldbuilding tools I would think this could be made without a ton of effort. I will also mention that Noxy (Current CEO of Hypixel Studios) did send out a poll asking on peoples opinions on a set of tools made specifically for this. While it was just speculation, it did come back with an overwhelming yes!
Well that depends. If the RPG is built in the game as a mod the yes! I'm not a Hypixel Studios staff, but according to their FAQ in late 2018 they give this answer...
Will I be able to monetize Hytale content?
You will be able to make your own Hytale content and services and monetize them. There will be a lightweight set of rules and guidelines regarding the creation of monetized in-game content, as well as some basic do’s and don'ts with regards to using our IP. These rules are aimed at improving user security, prohibiting extreme content, combatting scamming, and so on. They will be informed by drawing from our own experiences operating our server and consulting with community members. We are very confident that our guidelines will be easy to agree to. A core goal of Hytale is to empower and enable all sorts of content creators, and we want you to be able to support yourselves by chasing your passions.