If you are using ODS TAGSETS.EXCELXP it is not possible to insert a logo into a SAS-created file. For TAGSETS.EXCELXP it is because, by Microsoft design, Spreadsheet Markup Language does not support the inclusion of graphic images. For the TAGSETS.EXCELXP created file, you probably can insert an image after you open the file, but only if you save it as some file type other than XML.
With ODS methods, like ODS CSV, or ODS HTML or ODS TAGSETS.EXCELXP, you are just creating text files that Excel knows how to open and render.Your other alternative (to CSV or ExcelXP) is to use ODS HTML or ODS MSOFFICE2K and create an HTML file that Excel knows how to render. Excel may be more accepting of graphic images that are defined HTML <IMG> tags.
It really depends on how you are creating your file. The only part of SAS that creates a "true binary" .XLS file is PROC EXPORT (I'm not counting DDE methods here). Again, with a PROC EXPORT-created file, SAS would not even have the syntax to put an image into the Excel file because PROC EXPORT is all about getting the SAS data into Excel format.