Workgroup to Domain Hyper - V

Hi,

I have taken on a new domain and found that they have one hyper-v server (2012R2) which is running 2 domain controllers, 2 application servers and their file server which is serving 30 users. 

My concern is that the Hyper-V server in on the domain so there is the pertentional to be locked out of the domain. My intent is to put a second Hyper-V server in which will be in a workgroup and and one of these DC's on there or would you suggest this I create this second server as a DC and install the Hyper - V service on. 

Thanks

Wayne