I doubt that as well. The horn card mentions the Warlord using his ability, not someone else. Granted, the card might not have existed when FvW was shipped, but due to the wording it would IMO warrant a FAQ ruling stating that you can indeed use Gurmash with the horn.
How, exactly, do you propose that Gurmash use an item that the Warlord is holding (possibly in an entirely different zone)?
My statement was that I don't see that possible unless AW rule otherwise.
I am used to that games usually don't make sense. Like in LotR LCG equipping a hero with two armours at the same time and not being able to add him a weapon, because you have reached the limit for restricted items on him. So if AW ruled that some weird stuff such as this being possible, instead of burning the city in protest against an illogical ruling, I'll be like "meh, whatever".
Mind you that I know that here in MW things usually make sense (yeah, I know that magic isn't about making sense, but whatever) and my post wasn't just a desperate attempt to somehow try to make using Gurmash and the horn together possible even if it might have sounded that way. And no, I'm not even trying to put words in your mouth as the previous sentence might have sounded.
English just isn't my primary language.