I think the source IP is just for the tunnel configuration for GRE on the receiving switch.  When you setup a typical GRE tunnel you specify the src/dst IP or interface, i imagine under the hood, the ERSPAN session also requires the same information ...

Based on the destination not being a destination switch, Am i right in thinking that there is only the source switch configuration to consider in this instance? As the ERSPAN destination is an appliance, that appliance will simply receive the traffic...

Would this ERSPAN solution work from an SDA enabled EN to a non fabric router? For example, an ERSPAN session from an EN at multiple sites, back to a single ERSPAN aggregator connected to a DC switch? Thanks, J