ARS Sync, multiple servers with password sync

We have been extending our use of the Sync service and have noticed the server is bogging down.  We use it to sync a lot of attributes between AD domains but also some from SQL and other sources.  For some domains we also do some password sync.  I'm trying to determine if we can stand up a second Sync service and if it will cause an issue with password sync?  I know i can setup the workflows to run on both but I thought I recalled from a while back, that only 1 server can register in the domain as the server the capture agents send password changed to.