Well it seems more likely that he just has a diabolically efficient intelligence-gathering network that keeps him appraised of unauthorized excavations.
Although I can't think of many beings that would want to sneak into the Nine Hells to illegally mine. Maybe it's other devils stealing the plane's mineral wealth he's concerned about?
For what it's worth, I'm inclined to agree.
First because Ed Greenwood doesn't mention Adonides having any Ranger-like abilities
(e.g., as opposed to Bifrons, sort of, who has "a natural knack for navigating (knowing where he is, even on the Prime Material Plane, and intuitively knowing accurate compass directions)";
Dragon 76, p. 31).
And second because I've always thought of the Dukes of Hell as feudal lords of a kind lording it over their fiefs from their castles (or lairs, it's D&D after all) ever since I read Greenwood's utterly inspiring
Nine Hells articles back in the day. That also fits in nicely with their alignment and the hierarchical structure of "diabolic society".
Now, since Adonides is, of course, a vengeful and meticulous cretin, fighting to maintain his position like any other devil, in a position to command his lessers, and (last but not least) in charge of the security and internal stability of Caina, the notion of him having a diabolically efficient intelligence network seems inevitable.
As to who to protect the mineral wealth from, it wouldn't be a stretch to think of the many lesser devils of the Hells as "serfs" who incessantly have to strive to escape the oppression of their betters, to move upward in the hierarchy, and even to keep their current status. Details of this are best left to each individual DM but could include getting one's hands on (some of) the riches of the plane. This could range from lowly individuals or goups of them, to one of Bifrons' commanders engaging in a spot of unauthorized excavation to amass a stupendous amount of precious stones to get in his lord and master's good books (Bifrons collects gems;
Dragon 76, p. 31). And then, of course, there will always be the odd powerful PC and their associates deciding to go and see for themselves whether there's any truth to the rumors of the fabulous riches of Caina.
Why Adonides would appear in person is explained in
Dragon 76 (p. 29: "Adonides is naturally cruel and high-handed, and (...) the steward of Caina spends much of his time roaming the plane with a guard of 16 ice devils, searching for and punishing intruders and those who misbehave or act to betray Mephistopheles."). I would personally combine this with an unofficial love of "riding to hounds", which fits in nicely with his natural cruelty.
Just some thoughts.
By the by: whatever happened to 1E/2E abilities of devils in general
(e.g., induce
fear)?
.
