You can yes…you’re not required to use the widgetkit one. Obviously because there’s so many out there, it’s just a case of trying out the ones that you’re interested in. Please note though that every single slider that is available may not be 100% compatible with the curved graphic, but I know for most, it should be OK.
Perhaps I’m not understanding this… the Layer Slider is a paid slider plugin and then the free one that the front page of the live demo for Celestial Reloaded is using the Widgetkit one. Are you using any of these or a different one? How you use a slider depends on what slider as they all have different methods of adding a slideshow to a website. Some have widgets, some let you hard code it in a theme file, some do shortcodes….