Hello Piotr,
As your requests will come from the LDNS, maybe the way bellow, solves that issue:
GTM Server/VS:
server_DC1/vs_name (with some monitor)
server_DR1/vs_name (with some monitor)
GTM Pool:
pool_to_DC1_vs
LB preferred: Global Availability
Order 0: server_DC1/vs_name
Order 1: server_DR1/vs_name
pool_to_DR1_vs
LB preferred: Global Availability
Order 0: server_DR1/vs_name
Order 1: server_DC1/vs_name
Topology Regions: (IP subnet is)
region_DC1 { list of LDNS addresses }
region_DR1 { list of LDNS addresses }
Topology Records:
Region is "region_DC1" then pool "pool_to_DC1_vs"
Region is "region_DR1" then pool "pool_to_DR1_vs"
WideIP:
LB preferred: Topology
Pools:
pool_to_DC1_vs
pool_to_DR1_vs
Regarding balance methods, I think even when server as Generic Host, most types still can be used, but in your case, maybe "Topology" and "Global Availbility" types can statisfy your need.
This is what I can think for now.
Regards.