Hi, If you look at this link diagram you have inside side , outside switch , and the pair of ASA in the middle one active and other in standby, both interfaces are being monitored.
http://www.cisco.com/en/US/products/hw/vpndevc/ps2030/products_configuration_example09186a00807dac5f.shtml
The answer to your question is yes, you need to configured for each vlan subinterface or interface on the ASA a failover to have the interface monitored.
Example:
ASA_Primary: outside ip 172.16.1.1
ASA_Primary: inside_IP 10.20.20.1
ASA_Secondary: outside IP 172.16.1.2
ASA_Secondary: outside ip 10.20.20.2
interface Ethernet0/0
description outside
nameif outside
security-level 0
ip address 172.16.1.1 255.255.255.0 standby 172.16.1.2
interface Ethernet0/1
nameif inside
security-level 100
ip address 10.20.20.1 255.255.255.0 standby 10.20.20.2
interface Ethernet0/2
description LAN Failover Interface
interface Management0/0
description STATE Failover Interface
management-only
same principle above applies for asa subinterfaces if u are doing dot1q trunking.
failover
failover lan unit primary
failover lan interface failover Ethernet0/2
failover link state Management0/0
failover interface ip failover 10.1.0.1 255.255.255.0 standby 10.1.0.2
failover interface ip state 10.0.0.1 255.255.255.0 standby 10.0.0.2
Regards
PLS rate any helpful posts
Jorge Rodriguez