DocBoss header and footers set in the Main screen of your projects will not be applied to excel documents. However, DocBoss xls template variables can be used on SDI Excel template header and footers.
General variables can be used in headers and footers in excel.
As well as cover page variables to display information such as the Title and Document Number of the SDI itself.
Keep in mind, when using cover page variables, the information will not be placed on the headers/footers until the excel SDI is submitted. It is at the submittal process when DocBoss will add the information to the SDI.
Upon upload of the template, you will get a warning because you are uploading an Index template but using cover page variables, this is okay, press Yes to proceed. 
Below is the output result after the SDI has been submitted, using the variables shown above.
