Given that the conscious mind cannot reach the deep subconscious to know what it is thinking, how well does the deep subconscious monitor conscious thought and awareness?

The reverse is not true. The deep subconscious hears everything the conscious self is thinking and watches all the actions it undertakes. After all, the conscious self needs the body and so the subconscious mind is an important aspect always of everything going on from moment to moment. There are many automatic functions that are learned and have become a habit and will be carried out automatically, and a significant portion of that so-called "muscle memory" will be presided over by the deep subconscious always, to watch what is happening and to step in if there might be a difficulty or a mistake to prevent a problem from brewing. So the deep subconscious is surveilling the landscape on a continual basis and will be looking for trouble as well, as its charter is keeping the self safe from harm, and to do so it knows it must be vigilant and pay attention to detail because there can be danger lurking anywhere and many hazards that must be noticed and avoided.