NTP concerns for virtual NIOS grid?

[#1]

Recently switched from physical to virtual GM, GMC, and all grid members... The virtual grid is spread out across several separate VMware clusters around the world. I have several hardware-based low-stratum NTP server appliances available globally too. I'm not using Infoblox as an NTP server for any of the regular workload servers/VMs as they're pointing at the hardware based NTP servers.

Are there any NTP-related concerns for the grid I should pay attention to or changes now that they're all virtual? (<-- VMs are regularly snapshotted as part of a backup solution, so is that snapshot stun a concern?)

The Grid NTP Config is set to sync with my external (physical) NTP server appliances.

The Member NTP Config for the GM and all the other members do not have "Enable the NTP Server on this Member" checked. (<-- should the GM have this turned on?)

The Member NTP Configs for all the NON-GM members are all set to "synchronize this node only with the Grid Master". (<-- is that possible when the NTP Server isn't checked on the GM)

Would it be better to have all the member sync time with the virtual GM or have them all pointed  externally at the physical time server appliances?

[#2]

Is your GM in HA? 

If not I would point them externally.