It is not a must to have support for SR-IOV for FlexVNF to work.
VersaFlexVNF supports multiple I/O interfaces in the KVM environment
virtio
e1000
SR-IOV
The performance with FlexVNF with virtio interfaces will be better when compared to e1000 interfaces, whereas performance of FlexVNF will be much higher with SR-IOV interfaces when compared virtio/E1000 interfaces.