Yearn is completely decentralized and people from all over the world contribute both full-time and part-time to build, maintain, and improve Yearn and its products. Yes, YFI holders can decide what to do with the treasury and funds the protocol holds. Recently, they voted on YIP 56: Buyback and Build. This uses excess revenue to buy back YFI from the market which is used to hold, farm with, and pay contributors.
Yes anyone can be a Strategist. Strategists create strategies while protocol devs create and manage the vaults along with our Keep3r bots. We are working on better onboarding for strategists, but for now, this repository is a good place to start. The strategist multisig/group is responsible for maintaining, peer-reviewing & overseeing strategy creation, and monitoring production strategies. Strategies that strategists develop can go into production vaults if they pass tests/peer reviews. If a strategist has a strategy on a production vault then, yes, they earn the 10% strategist fee from the revenue that specific strategy manages, but currently, it is split amongst strategists in a fair way they have decided on. If a strategy is successful and well tested then it can be generalized to other vaults.