I looked at the eSATA port on my P8Z68-V PRO and it does not look like an eSATAp port which is powered. It just looks like a standard unpowered eSATA connector. I don't see any USB pins on that connector so it would have to be unpowered.
Where have you read that this port is powered? I would like to know this, for my information, too.
The data signals portion of the port itself is controlled by the JMicron JMB362 Controller and requires the installation of a device driver.