I think you're wrong. VSAM files are disk oriented files. You can back them up and restore them, but you cannot access them directly from tape as you can with flat file.
Think of what goes on when you access a VSAM file. The indexes can be separate files, as the data cluster is. When you access a record on a VSAM file the index is searched then the data is accessed. Tape is not designed to forward and backward seaching for data as disk is.