I would suggest a support ticket.....Very odd you would get this error here.  I will look for some reasons, but I doubt I will find anything.   Since you are Oracle, you are unlikely to be educational, which means your support agreement should include such cases.  If the case appears to get stuck in support, let me know as well as the case number.

case is 02888204-ZRS data source connection failed Oracle

Support asked me to reconfigure domain configuration.

But didn't help ( I use the zone manager option not the resource file option).

results in same error message. I can connect to the zone over 7443, could connection from ZRS to database server be the cause? Do I need direct connection from ZRS to database server, maybe look into that?

If you are not getting the help you need.....Please Ask for it to be escalated.  

I see your Support Engineer did request and get a Sr Engineer to assist.  This person would be the ideal person to help, but perhaps it will be useful to have the case directly assigned if things appear to be dragging.