The list of documents required for processing the entry visa-D for family reunification purposes can be found from the below URL: https://www.vfsglobal.ch/switzerland...doc_220115.pdf
Almost at the end of the pdf file, you can see "The Embassy reserves the right to ask further documents if necessary
" and hence police clearance certificate (PCC) might be one of those documents which may be asked depending on the applicant and the processing officer. However it is not usual to forward it in the point of application (in your case, New Delhi).
You would have to forward the PCC in Zurich Migrationsamt office along with a list of other documents like work contract copy, rental contract copy etc. Immigration authorities in Switzerland almost always like to have all of the relevant documents on hand before making a decision. Hence start working on getting a PCC for your spouse since it will be required soon. If you don't have the PCC ready by then, expect further delays in the visa processing.
FYI, a detailed description of the different steps involved for the family reunification visa-D is given in an earlier EF thread: Dependent visa, Permit B for spouses wanting to reunite with family in Switzerland