Re: ESRS Gateway and Policy Manager
The ESRS Gateway needs to be on the same network as the VMAX and any other EMC equipment you may have and could potentially be at a physical location different to the location of the EMC equipment, so your choice really.
In your situation, what would make sense would be an ESRS Gateway at Prod and another at DR in an HR configuration. We would also then recommend a minimum of one Policy Manager again on the same network.
I could also get someone from your local EMC team to contact you for more information if you would like?