The fact NSX-Edge LB terminates SSL means NSX-Edge LB can modify the HTTPS client request (like add XFF header).
Note: Like NSX-Edge LB can do for HTTP traffic.
The fact NSX-Edge is configured in transparent mode (= no SNAT)
(and this whatever if that's HTTP, or HTTPS Passthrough, or HTTPS END-to-End SSL, or HTTPS SSL-Offload, or whatever)
means the sce-IP client (at the layer3) will NOT be replaced by the Edge-IP => the backend server can see the real client IP@ in the source-IP@ of the traffic.
Attention: Transparent mode requires the servers default gateway to be the Edge.
Dimitri