In our Active Directory domain, we have a handful of SharePoint farms, mostly SP2010, and an SP2013. Our main farm, an SP2010 Enterprise farm, has User Profile Sync Service configured and actively running. There is no publication/subscription going on to other farms.
Because of the extraordinary pain and misery I suffered to get UPSS functioning properly, I have been loathe to even attempt to fire up UPSS on any other farm, although it would do us well if this were possible. Some of my concern is just pain avoidance, some of it is a worry over accidentally setting up some awful three-way endless loop of updating between different SharePoint farms and our Active Directory.
I have not been able to find any authoritative statement on activating multiple UPSS instances in a single AD domain. Fwiw, our AD domain function level is 2008.
Can I safely run an instance of UPSS on more than one of our SharePoint 2010 or 2013 farms in our Active Directory domain?