isn't it strange that Jaruzelski became a general then in a "people's" army?
No, it isn`t. There were more Red Counts in communist ranks. They were watched over with suspicion until they proved themselves worthy of communist trust. He deserved it by working as a secret agent in 1950s and never ever betrayed communism.
but, joined uprisings when called (On Poland's side of course)
Yes, they did but it was later on, when noblemen who had initially agreed to Russian partition saw that it wasn` t so rosy after all.