Hi,

Was the OS installed while connected to the R730? The correct chipset drivers may not be installed. 

No, we are setting up the OS on a USB device to use as the boot disk.  We created the boot USB and VHD as per the Microsoft Instructions here 

https://technet.microsoft.com/en-us/jj733589(v=ws.11).aspx

Is it possible to inject the missing drivers into the VHD file so we can boot from the USB into 2012R2 Hyper-V?

Here is the chipset driver. http://www.dell.com/support/home/us/en/19/Drivers/DriversDetails?driverId=3X9CG&fileId=3598947457&osCode=W12R2&productCode=poweredge-r730&languageCode=en&categoryId=CS