Alexandr,
I suspected that this would spark some additional questions.. 🙂
Anyway, yes the purview engine will collect the flows and there is nothing else you need to do. To check to make sure you are seeing the flows, on the management interface - example: tcpdump -i udp port 2075 - You should see flows from the switch.
As to the mirror, for testing I suggest directly collecting the mirror to the appliance. We dont support the GRE tunnel method at this time on XOS but we do support R-SPAN. I will post the R-SPAN configuration in a later post here.
Bill