vNIOS for Hyper-V is not recommended as a Grid Master or Grid Master Candidate. Specifications

DNS forwarding proxy is not supported on any appliance that is running on a memory lower than 4 GB. source

There might be a significant performance impact on your appliance and network during the DNS forwarding proxy installation process depending on the network connectivity between NIOS and BloxOne Threat Defense. Every node will have to install the DNS forwarding proxy before serving DNS recursive queries, which includes the HA nodes. source