Yes R reports can have an associated meta-data file. The XSD is in the /schemas/ directory with the name report.xsd. The format is the same one we store in the database when you create an R report via the web user interface. I don't have an example handy, but if you create an R report and then look in the core.report table in the descriptorxml column, you'll see an example.

The main reason you'd want to use a meta-data XML file is to adjust the reportType property. Some of the views in the study module will show only reports that have the specific report type of "Study.rReport".