Alright, here is how puppets work. As NPCs, the master has basically total control with their country with the exception of government.
Puppets as PCs are allied to their master nation, and may make their own independent decisions. Puppets played by actual people are merely influenced by their master, they may command their military, control the economy, and spend what they want to. The master in this case only can influence PC puppets.
However, if puppets stray too far away from the master's policies, they can be, 'brought back into influence', usually meaning a crackdown on dissidents or for extremely unruly puppets, annexation.
Now on to questions.
Jopa: Serbia is still on the map because Austria-Hungary could not control the territory due to extremely high nationalistic dissent, as well as other areas like Croatia. Consequently, these areas were given independence by Austria-Hungary, albeit with puppet governments. Serbia is a special exception, which had eventually broken away from Austria-Hungarian influence. It is extremely unlikely that they will unify, or be held under control by Austria-Hungary or her puppets.
Serbia's dissent is in the stats. They are not powerless, they have a relatively good military compared with Austria-Hungary's puppets.
Charles Li: I'll grant this, just be forewarned that you should try to follow German suggestions and be In Character as your nation.
