wysiwig editors are frontend, and don't have any relation to the framework. That just sees a posted textarea come in. So any one will do, depending on your requirements.
If you want to validate HTML, you can clean it using \Security::xss_clean($var);
It uses the Hmtlawed package (which is included in fuel/core/vendor) to scan and clean the HTML. If you want to have custom cleaning rules for Htmlawed, you can pass them in the second parameter.