Excerpt from the travel diary of a celestial planar explorer:

The rilmani... are a very old race. Native to Acheron. There are three kinds of rilmani; three strains in their culture, their thought. Aurumachs, cuprilachs, and ferrumachs - gold, copper, and iron. This divide has spawned many interesting theories about the history of Acheron...

All rilmani believe in... balance. Stability. Order. The aurumachs believe in order through peace and unity. The cuprilachs believe in the balance of opposing forces. And ferrumachs believe in order through extermination of chaos.

Once, the three races of rilmani were balanced, in numbers and in influence. But as time went on, the aurumachs and cuprilachs declined, until eventually there were almost none left. Only the ferrumachs remained.

The rilmani have not participated in any conflict for a thousand years, and haven't been major players on the cosmic stage in twice that long. That last conflict was a war between rival demon lords...

The domain of the rilmani is so distant that no means of planar travel reaches it directly. Some cubes have long paths that take them to the edge of rilmani space; and occasionally the curious or foolish traveler will mount an expedition there. Those who return bring back reports of a race totally prepared for war, and without the self-destructive tendencies that make humans turn on one another in the absence of external conflict. The rilmani only train... and wait.

Vasily and Nikolai's analysis of the "one mind":

Acheron is a plane that is fundamentally aligned with law. As such, creatures native to Acheron have a lawful mental outlook, more pervasive and deep-set than any lawfully aligned mortal from Midgard?. For creatures who arose in Acheron, or who have dwelt there for many generations, or those who have "gone native" in a fundamental way, this is reflected in the fact that creatures of the same type think and act in predictable, non-chaotic ways, and more importantly, in the same ways as their fellows. They instinctively do not see themselves as individual creatures but as the same creature as nearby others of their kind. Because Acheron natives also typically have various forms of enhanced senses, communicating by scent, vibration, and other, more exotic sensory modalities (including a form of very simple telepathy widespread even among creatures of near-animal intelligence), they are able to, effectively, act as one whole. For instance, it's impossible to surprise, flank, hide from, or otherwise fool an Acheron creature unless you fool all nearby others simultaneously. All of this is a manifestation and effect of the lawful nature of the plane and the influence it exerts on the nature of its inhabitants.

The rilmani "one mind" is, you surmise, some sort of telepathic technique that taps into this instinctive "group-mind" tendency. It's possible that the rilmani figured out how to develop this ability in their creations (such as the maugs?), and how to adapt it to the various sensory/communication modalities used by the various creatures of Acheron, essentially giving themselves the ability to join, and exert control over, the shared mental/instinctual group interactions of native Acheron creatures.

As for emulating or duplicating the "one mind" effect, that would be difficult; having telepathic ability would probably be a start.