Unfortunately, the 31108PCV switch does not support NetFlow. The fact you saw the NetFlow feature printed out in the show feature is in fact a cosmetic defect only; that feature should not have been listed there at all. The 7.0(3)I7(5) does not report this feature anymore:
N3K2(config)# show ver | i NXOS|Chassis
NXOS: version 7.0(3)I7(5)
NXOS image file is: bootflash:///nxos.7.0.3.I7.5.bin
NXOS compile time: 8/28/2018 2:00:00 [08/28/2018 09:51:46]
cisco Nexus 31108PCV Chassis (Nexus 9000 Series)
N3K2(config)# show feature | i flow
openflow 1 disabled
sflow 1 enabled
N3K2(config)# feature n?
nat Enable/Disable NAT
netconf Enable/Disable netconf Services
ngoam Enable/Disable ngoam
ntp Enable/Disable NTP
nv Enable/Disable VxLAN
nxapi Enable/Disable nxapi
nxsdk Enable/Disable nxsdk Services
I am sorry to disappoint you; you will not be able to start NetFlow on this platform (in fact, no N3K platform currently supports it).
OpenFlow is an entirely different and unrelated mechanism; it is not used for traffic statistics collection but rather to control traffic forwarding entries in the hardware. We should not talk about OpenFlow in relation to NetFlow at all; these two are entirely different things.
My apologies - since you have been talking about the two unrelated features in the same thread, and did not really clarify what exactly are you focusing on with the OpenFlow, I was not sure if you were confusing the two. I apologize - I meant no offense.
Maybe it would be better to open another thread just for the OpenFlow issue you are looking at.