I’ve asked in General forum for advice first but didn’t get much out of it so I decided to post it as a bug.
The Arreat’s Face helmet is intended for Barbarian only (written in red) and the Act 5 can wear it so he’s obviously a barb or he would not be able to equip. Then this mean the stats that are also for Barbarian only should work, this +2 Combats skills and + 2 Barb skills. As it is now it’s not working.
Dbrunski in this video is telling it add skills now I don’t know him much but I saw @Diablo on twitter link to him in the past so they must trust him somewhat?
Then there is this D2R guide at (hZZps://fr.wowhead.com/guides/diablo-2-mercenary-item-builds-runewords) at the bottom of the page saying:
Besides the usual armor and helmet picks, Arreat’s Face is the only class-exclusive choice here. It adds tons of +Skills for an Act V merc that uses both Bash and Stun regularly, and just serves as a great all-around pick if you’re looking for excellent defense and survivability.