Using ODS MSOFFICE2K, you are NOT creating a "true, binary" Excel file. ODS MSOFFICE2K creates Microsoft "flavor" of HTML tags. Both Excel and Word know how to open and render HTML files. Calling the output file as .XLS does not make the file a true,binary Excel file. Using an extension of .XLS just fools the Windows registry into launching Excel when you double click on the file name.
I do not know how you create zip files or zip archives on the mainframe. As you have discovered, emailing the HTML file created by ODS MSOFFICE2K should work fine. If you have questions about creating a zip archive on the mainframe, you might want to work with Tech Support.