though, like the Geth, I get the sense the Sleeper drones have multiple layers of 'intelligences' within them, likes cells in a body, kept in check by a network of failsafes. The 'brain' of the drone is the AI Nexus, clearly a self-contained and autonomous system that controls the larger system.
The drones also learn and stockpile information like humans do, enabling adaptive tactics development.
However, like the Movers of Homeworld 2, they're still bound to their original purpose, and continuously focus on it, like an obsession.