I´ve use JS libraries inside Vaadin (e.g., d3.js) with no problem (once you know how to do it). There are many good JS open-source libraries that it is difficult to avoid use them. One of them is the React-diagram https://github.com/projectstorm/react-diagrams that I like it very much.
What I´ve tried without success is to use a LitElement that wrapps a React-diagram component. Mainly because I don´t know React JS.
Any idea is welcome.
PS: All the examples I´ve found so far are the opposite… using web-components inside a React project.