Just to set the scene for discussion, You asked the following on CSCO forums
This is what I would like to achieve:
1/- All 300 sites configured with the ip helper command to send each client request to both DHCP servers at the main office.
2/ - If the main office blows up, have all client requests to go to both server IP addresses at DR
(1) is possible to achieve with JUNOS BOOTP helper feature. Sample configuration (where servers and clients are inside VRF)