You can use the css out of the box.
The html layout if you are planning on using it will need some adjusting if it depends on external js libraries.
You also will have to change custom components they nornally use for Wappler AC ones.
This is not a plug&play thing but you can perfectly use them. And there is absolutely no way for Wappler team to make them plug&play for the exact same reason you will normally find that for the same theme there are html, angular and react versions.