This depends on the application mapping. If the application is mapped to LAN IP address on the back-end servers then application will be accessible using LAN IP address and you need to use LAN IP address in the pool. And if application is mapped to MGMT IP then you need to use MGMT Address. If application is accessible using both IP addresses (LAN & MGMT), then you can use any of the two IP addresses under pool.
Hope it helps!