Hi Jared. There are currently three Ultimate Inventory System (UIS) integrations: Ultimate Character Controller (UCC) including all its variations, Behavior Designer (BD) and Player Maker.
There is an integration for Pixel Crushers Dialogue System in the works which Tony Li is working on.
There are plans to integrate with UMA and the Localization package in the future. There are also plans to integrate with popular network solutions like PUN some time next year.
If you wish to integrate the asset with something particular feel free to create a new thread under UIS -> Integrations category and I can help you with any issues you encounter.
As for the docs, if you have any feedback on things we could make more clear do let us know, we keep adding content over time