First of all I would ask if vROPS is really needed in DR. In a DR scenario what is the real use of vROPS? What should be done.
Second, if you want vROPS in DR you need to understand the following:
vROPS measures vCenter objects, each object is a moref (managed object reference) that is unique to the vCenter. The VM in your protected VC is not the same as the failed over one. So if you fail over the objects that vCOPS will be monitoring will be the place-holder VMs that were created when you protected the VM. So the only think that vROPS can do for you in DR is to see the CURRENT details, forecasts, trends, KPIs etc will only come into itself after at least one week (more like 3-4). If you are 3 weeks in DR...something went seriously wrong.
So if you want to measure and view the current trends then I would suggest 2 vROPS installations.