The speculation is just that ,speculation. The top secret context is just how things were titled or the paper work control of the facilities.
Many of the students and population were involved in industries that had an element of don't say too much.
For me the reality is the population heavily engaged in the sport of tourism, going back many year's all over the soviet union. The hike and route is completely standard to what everyone else were doing .
The assembly of for the dyatlov was completely random. Certain individuals were going to join but had to pull out for other commitments, then others applied and so on.
There are no hidden bases or anything of interest on the route , it's basically inaccessible by machine for hundreds of miles, it's by foot, ski, sledge or helicopter to get to these mountain tops.
Why a spy would be bothered to be on a hike with students going to the middle of no where to interfere with a grade 3 certificate for its participants carries little motive.
Personally I see no link. Fatalities from these hikes were not unique over the years. They are documented in many archives and training manuals.
If he was working as a spy , I don't think it has anything to do with the hike, he was using his time off to do what he enjoyed.