In Fushion the extended ports appear just as a line card to the main chassis. So they don't really run independently for configuration.
Right now PTP only appears to be supported on MX and ACX by the information in feature explorer. So if your main device is the MX of a supported platform and PTP feature you can run this on the Fushion setup.
Steve Puluka BSEET - Juniper Ambassador IP Architect - DQE Communications Pittsburgh, PA (Metro Ethernet & ISP) http://puluka.com/home
On a different but related note, I recently confirmed with support that although satellite devices are supposed to be considered line cards in a Fusion configuration, creating an ae interface across two different satellite devices is not supported yet. There are plans to do this with a future version of 17.x supposedly.
I have not personnally tested this but will whenever time permits.