A contract
I am a peacemaker and a diplomat,
Peacetreaties and trade deals are signed into law
a silent watcher to prevent betray.
Obviously contracts don't speak, and you can't break them
I’m hiding friends behind my body
Hiding smallprint in the body of the text
and make the rules for you to play.
A contract is a codified agreement on what the two parties can do
I can be clear or ambiguous, even graphic.
Can be plain, vague, or explicit; depending how it's written
But when it comes to work, I am snob,
Contracts play a huge role in business
my role is rather .. choreographic
A contract doesn't do anything on its own, it just tells other people what to do
while my buddies do the job
Could refer to lawyers, or the smallprint referred to as 'friends' earlier in the riddle