Well not really, there is still no logical way a man shouting will effect a horse, regardless of where he is. However a hero is more likely to respect an Arch Lector than he is to respect a normal priest.
However it suits WAAC players not to be logical.
You SIR!!! have insulted the intelligence and piety of my horse!
Rusty, my faithful steed, charge forth and dispatch this brigand with much hatred!!!
On a more serious note, its not unheard of for horses in battle to get worked up. There's a bond with horse and rider. If the men are all riled up then sometimes the horses do too.
And remember, the righteous fury isn't just the words from the warrior priest, they are
magical words.
Post FAQ, the war alter is worth it in your army if you have alot of mounts. And the fact that warrior priests get targeted like crazy in combat helps with deciding to take a war alter.
But then there is also an argument to just take a hurricanum for the +1 to hit since its affected every turn. And the hurricane is a fraction of the cost.