It will be a good factor if you have knowledge in web developing and there are a lot of tools that has been helpful and good through the web. Digital marketing is a different forte and its about marketing your products but having knowledge and background for both will be good.
I just found your idea of doing a certification, I thought I would recommend you the digital marketing certification course from Edureka which will help you achieve your goals at ease. Please go through the course details in the link below.
https://www.edureka.co/digital-marketing
http://unbouncepages.com/edureka-digital/
Good Luck.