I think we are taking about 2 different issues here.
1. As for the network card, you would be on the safe side to check if that card is on HCL (is this physical NIC or nested ESXi?)
2. As for MTU size this is configured when preparing host for NSX.
Once configured a this will create VMkernel port on each host in the cluster as the VXLAN Tunnel Endpoint (VTEP) with the specified MTU (1600 default I believe)
Working with NSX - Configuring VXLAN and VTEPs - Wahl Network