F5 DNS and two Service Providers

Yes, because what we are polling is the SP router's gateway which is most of the cases will be active, but the SP network will have an outage. This is because the pool that I have defined as a default gateway is just monitoring the SP default gateway by ICMP. So the links defined in the F5 DNS module ask the LTM module for the status of the default GW only via ICMP.

So if one of the default gateways in the GW pool is marked down by the LTM, the DNS link will be marked down. On the DNS module side, any wide-ip pool members on that link will be marked down, hence the failover happens.