Can Case Support Settings like Default Case Owner, automated case user be migrated from sandbox to production using ant migration tool by just including case object or they need to be migrated manually ?
Yes it can be migrated as metadata is available for case settings
<?xml version="1.0" encoding="UTF-8"?> <Package xmlns="http://soap.sforce.com/2006/04/metadata"> <types> <members>Case</members> <name>Settings</name> </types> <version>35.0</version> </Package>
Anything that has metadata available will be migrated .More info refer metadata guide
To overcome the difference in owner ,Manually find the XML file for case settings .It will be under settings folder and casesettings file and modify the User owner as relevant to PROD