Only requirement is you create a INLINEHTML field in a suietlet and add a div with a fixed id, use some webpack magic and write a JS file like this for the react app:

import React from "react";
import ReactDOM from "react-dom";

import Title from "NetsuiteUI/Title";

const Index = () => {
    return <div>
        <Title>Hello World</Title>
        <div>Hello React in NetSuite!</div>
    </div>;
};

export function init() {
    ReactDOM.render(<Index />, document.getElementById("netsuite-ssp"));
}