Yes, you can use the Accordion plugin with React as long as TinyMCE is version 6.5 or higher (https://www.tiny.cloud/docs/tinymce/6/accordion/). The version number of react-tinymce (4.3.0) is irrelevant.
The version number for the React Component is different from the version of TinyMCE itself (https://www.tiny.cloud/docs/tinymce/6/release-notes/). The component is a thin wrapper around TinyMCE to make it easier to use in an React application.
You can see what version of TinyMCE is on a webpage by entering this into your browser’s JavaScript console:
tinymce.majorVersion + "." + tinymce.minorVersion
Or, if you are using the Help plugin, you can check TinyMCE's version by selecting Help from the menubar, then clicking Version.