TLS Security profile there is an option called "Protocol packet header policy in TLS" which has three possible values "Unused" (Default) "Used" and  "Detect. While running interoperability tests we only got successful connections with "Used" and "Detect" options selected, while selecting "Unused" we only managed to make successful connections to another Axway Gateway.
1.What does this different options really mean?
2. What is recommended for maximum interoperability with other OFTP 2 certified products such as Odex, Seeburger, SAP etc?

This option has been introduced only for internal programming reason. For some protocol, the network header buffer (if there is), is managed in protocol level, for others, it is managed in network level. So the option is necessary in TLS profile to deal with these differences.

For OFTP 2 over TCP, the TLS Header Policy must be set to USED (or DETECT, but mustn't be UNUSED).