Does DNS Failover have a feature to prevent the primary IP from being put back into service when it comes back online?

Yes. Our DNS Failover does have a feature to prevent “Auto Rejoin”. Unchecking this box (shown below) for any of your servers will prevent it from automatically being used again when it comes back online.

This is often necessary if, after a fail over, you need to synchronize back-end data (such as a database) to the primary and then bring it back online manually.  To bring it back online manually, open the Failover Entry and check the ‘active’ check box (which will be unchecked, since it was taken out of service). NOTE: the server must be testing and show a green icon prior to making it active again, otherwise despite checking the ‘active’ checkbox, it will not come back until it successfully monitors again.