It's a very common pattern for hedging an opinion, can be interpreted I think X. Because this pattern is used to express subjective opinion, the subject is almost always "I" and usually dropped.
More concretely, a direct translation of the sentence in question would be something like
However, (I) don't know for sure if the real protagonist of <미치지 않고서야> is the company which is a social organism of mixed desires and motivations.
But the speaker is actually trying to say,
However, I think that the real protagonist of <미치지 않고서야> is the company which is a social organism of mixed desires and motivations.
Notice that the sentence has subordinate structure, and the subject (or topic) of the subordinate clause is 주인공, while the subject of thinking / not-knowing (main verb) is dropped.
Without -도, this hedging pattern barely works, and when it works it works in the opposite way. Let's take a set of examples from the page the OP linked.
- 엄마가 올지 모르겠어요 = I don’t know if mom will come
- 엄마가 올지도 모르겠어요 = I don’t even know if mon come will come
I actually think the second sentence above is another hedging expression. Of course, the translation above is accurate, and you can use -도 for emphasis in this case, but it sounds more natural as a hedge than an emphasis. Thus, in the second sentence, the speaker actually thinks mom is more likely to come, or at least s/he wants the listener to think that s/he's pretty sure their mom will come. On the other hand, without -도, the first sentence could be merely a factual statement (that the speaker is uncertain about what to happen in the future), or even sometimes it carries somewhat negative nuance, often with a sense of resignation or frustration. So with that subtle difference in mind, the same set of sentences can be used for different hedging strategies.
- 엄마가 올지 모르겠어요 = (I really wish she's here but) I can hardly think mom's going to make it.
- 엄마가 올지도 모르겠어요 = (I didn't expect but) I think mom's probably coming.
Now, going back to the howtostudykorean lesson, the mom examples are followed by more examples with or without -도. If you take a close look at them, you'll see they have one thing in common; all of their embedded clauses are interrogative (notice interrogative words - 무엇, 왜, 어떻게). As questions cannot be statements or opinions, -지도 모르겠다 pattern in those sentences cannot be hedge, and only can be emphasis on the uncertainty.
Lastly, I want to point out that, just like many other linguistic phenomena, there are no strict rules when applying the patterns and usages above. To that end, I want to leave this last example here. Suppose two thieve are robbing a store, and one is saying this to the other who's cracking the safe.
빨리 해, 경찰 언제 올지 몰라. = Hurry up, the cops will soon storm in.
