There are cases when IKE local-out traffic needs to match a configured Policy Based Routing.
Since FortiOS 6.4.9, 7.0.2 and 7.2.0 a new, per VDOM, option was introduced:
# config system setting
set ike-policy-route enable | disable
For a PBR match, the firewall must have a valid route to the remote gateway.
More information about Policy Based Routing: