Since jenkins v1.607,
a slave definition is saved on "nodes/(slave name)/config.xml".
What's new in 1.607 (2015/03/30)
Refactor the Queue and Nodes to use a consistent locking strategy (issue 27565) Note that this change involved moving slave definitions outside the main config.xml file. If you downgrade after this, your slave settings will be lost.
But, thinBackup does not backup nodes directory.