Sorry! but the marriage certificate is MANDATORY !!! If check r10 completeness checks you would see how the Officer's asses your file. Which State are u in India...
I have been asking this question for a very long time. From what I came to know is that it's not needed for them to be added under IMM 8000 but we will need to add them under Family form.
If there is anyone who wants to add their spouse to the application Reply to me pls I could share whatever information I got with you. I have been doing a couple of research I may be wrong but hoping it would help people to some extend.