If the whole idea is to reward quality posing users, and slow spam down. Then farming for it, or giving it to someone just because they are your friend should be against the rules, however would be hard to prove. So it is likely just unethical.
Technically so, but if the case is only one and the post which got Merit is done well. i think this time there will not be any questions to those person who gave a merit to a friend. Am I wrong? I see that many of quality posts do not get even one Merit and here on the board we have a lot of examples when Merit was given to one line posts and something simple.