We certainly want people to be able to use ads on apps, although this
is going to be a per-container policy decision. Google will be
releasing an article about monetizing applications in Orkut to help
out with questions like this. For the time being, I'm not sure that
it's worth implementing AdSense in the closed Orkut sandbox, though.
You could just use a placeholder if you need to design your UI around
this.
~Arne