Setting up a test environment for 10.2 that is Hyper-V Environmnet, would that be ok?
I would imagine so we still run a lot of Gen1 Vms that came from 2012 (not our ERP though we rebuilt that when we went to 10.2.200) here but honestly I wouldn’t run anything on 2012 anymore with how far HV has come especially in 2016. I don’t know your situation either but Clustering in 2012 is sketchy at best so if you wanted to do that don’t plan on it. What is preventing you from upgrading to a 2016 host and using Gen2 vms?
Now if you mean just testing on 2012 have at it, if you mean going live on 2012 HV I would advise against it.