Bridge validators are separate from chain validators, and currently composed of a subset of Gnosis Chain validators. This is a dynamic set, as the bridge governors can vote to increase the current set as well as propose and vote on other bridge related measures.
Organizations are represented by an individual within that organization who is responsible for node operation & validation duties and/or participation in governance.
A governing board is responsible for voting and enacting all decisions related to bridge changes such as upgrading bridge contracts, extending the validator set and updating bridge parameters. Learn more here.