ULL ports can be use for forilink interface fortigate 600F

Hello Community, 

I would link to know does ull ports (x5-x6) can be use as fortilink interface in production? 

I am bit confuse because of this official document mentationed that x1-x4 can be use for the fortilink however I also read some other doc mentatined that any port can be use for the fortilik.  And ull ports are not part of the Integrated switch fabric. 
https://docs.fortinet.com/document/fortigate/7.4.12/hardware-acceleration/589036

Fortigate 600f: v7.4.12

Manage Fortiswitch:7.6.6

Can some expert please confirm on this, 

I appreciate your guidance here.