Yes. IntelliGantt has a notes field that is called Notes.
Of course, it is not rich text right now because we don't have a coverter for turning rich text format in to SharePoint html and back again. We're currently evaluating tools to use that will enhance the product.
You'd think Microsoft would supply a handy library to turn SharePoint HTML 'rich text' into their windows recognizable 'rtf', but its turning out to be more work than expected.