No it's not required of course. Responsivizer has been made to accomplish a mobile migration of your desktop site using admin tools.
All basic operations like reassign modules used on desktop template, colors, fonts, menu management, images upload, slideshow, etc can be done exclusively using available admin tools.
In some cases to accomplish optimal results may be needed some basic CSS knowledge, to add or change some styles in the main css file used by mobile template.
If you need to edit the main css file used by mobile template, you can use directly the integrated editor included in Responsivizer