FortiGate-6000 supports most FortiOS IPv4 and IPv6 ECMP functionality. Before setting up an ECMP configuration you need to use the following command to configure the DP processor to operate with VDOM-based session tables:
config load-balance setting
set dp-session-table-type vdom-based
Once you have enabled VDOM-based session tables, you can enable and configure ECMP as you would for any FortiGate.