Allied Leaders

My question is, do allied leaders have impact upon the host armies units?

In the scenario “Sorauren French Left” the British have units of allied Spanish and a Spanish leader in the field. I would expect Wellington’s leaders to be able to influence the Spanish units but can the Spanish leader influence the British ones? Historically I think not. But how does this work in terms of our game?
 

All leaders and units for the nations you command are considered friendly. Unless the Scenario Special Rules prohibit it, one nation's leader may attach to any other national units that you command.
And all units on the same side as such a friendly Leader, benefit all bonus of this Leader.
www.commandsandcolors.net/napoleonics/th...in/faqs/leaders.html

Historically this level of allied cooperation seems unlikely. Most nations didn't like foreign generals, even without  a language barrier. British and Portugese seem to have got on, and Russian and Prussian through force of circumstances in the 6th Coalition. French was widely spoken, but Napoleon didn't elevate many foreigners into the Marshallate (just Pontiakowski by recall). 

Thank you for the reply.

I have just finished reading “To War with Wellington” by Peter Snow.
In that he mentions Wellingtons distrust of allies both in the peninsula and at Waterloo. Although, as you say, respect grew between the British and Portuguese.