Is it common for higher education institutions to offer sabbatical periods for administrative / support staff?
Large Land-Grant University in the U.S.:


  Applications for professional leaves will be considered only from faculty members on permanent appointment (academic or annual) who have completed at least five years of active service for $UNIVERSITY at the time the leave is to be effective.


Another university in the state has a very similar policy. Beyond that, I have never heard of staff taking sabbatical leave. Occasionally going for professional development, etc. but not for that length of time.