GTM monitoring a link

The short answer is YES!

For reference, I tested this on 13.1.0.7.

If all Links assigned to a DC fail (i.e. monitors fail):

1. GSLB (Wide IP) Pool Members in the Disabled DC are immediately marked down. This may result in Wide IP Pools and Wide IPs to be marked down.
2. GSLB Servers in the DC are immediately marked down. GUI shows Red: "Offline (Enabled) - No enabled VS available".
3. GSLB Data Center (DC) with the assigned link(s) is immediately marked down. GUI shows Red: "Offline (Enabled) - No enabled servers available".

Example Logs:

Monitor instance /Common/snmp_link 10.20.0.1:0 CHECKING --> DOWN from 10.30.102.1 (DOWN)

SNMP_TRAP: Link /Common/dc1_link (ip=10.20.0.1) state change green --> red ( Monitor /Common/snmp_link from 10.30.102.1 : DOWN)

SNMP_TRAP: VS dc1_test_https_vs (ip:port=10.20.100.200:443) (Server /Common/dc1f5a_b ) state change green --> red ( Inherited red from parent link /Common/dc1_link.)

SNMP_TRAP: Server /Common/dc1f5a_b (ip=10.30.102.1) state change green --> red (No enabled VS available)

SNMP_TRAP: Data center /Common/DC1 state change green --> red (No enabled servers available)

SNMP_TRAP: Pool /Common/test.example.com_gslb_pool member DC1_SAML_IdP_HTTPS_VS (ip:port=10.20.100.200:443) state change green --> red ( Inherited red from parent link /Common/dc1_link.)

SNMP_TRAP: Pool /Common/test.example.com_gslb_pool state change green --> red (No enabled pool members available)

SNMP_TRAP: Wide IP /Common/test.example.com state change green --> red (No enabled pools available)

If all Links assigned to a DC to are set to "Disabled":

1. GSLB (Wide IP) Pool Members in the Disabled DC are immediately marked down. This may result in Wide IP Pools and Wide IPs to be marked down.
2. GSLB Servers in the DC are never marked down. GUI shows Green: "Available (Enabled) - Available".
3. GSLB Data Center (DC) with the assigned link(s) is never actually marked down. GUI shows Green: "Available (Enabled) - Available".

Example Logs:

SNMP_TRAP: Link (/Common/dc1_link) disabled

SNMP_TRAP: Pool /Common/test.example.com_gslb_pool state change green --> red (No enabled pool members available)

SNMP_TRAP: Wide IP /Common/test.example.com state change green --> red (No enabled pools available)

Monitor instance /Common/bigip 10.20.100.200:443 UP --> DOWN from /Common/dc1f5a_b (no reply from big3d: timed out)

Monitor instance /Common/gateway_icmp 10.20.0.1:0 UP --> DOWN from /Common/dc1f5a_b (no reply from big3d: timed out)