Is it necessary to do the entire six sigma certification?
Six Sigma will help move your company from being a good company to a great company. It is customer centered. You can learn more with six sigma training and certification. There are many good resouces available online to aid your training.
It's certainly useful if you're applying to an organization that is looking for project management or even more so, an organization that uses Six Sigma. The concepts don't need the whole organization to be on board and if you know it and can explain how you've applied the theory, it's a nice selling tactic on how you can benefit the company.
i've been writing professional resumes and cv's for job seekers for years. Six Sigma is one of many highly regarded accreditations/skills to have on your resume. as for "is it neccessary to do the entire six sigma certification" - not sure to the extent of the course you are doing, but it's better to be certified than not.