All it does is tell us whether or not Paynims turn up. Once they turn up, it says nothing about what they do, whether they find the hidden PCs, etc.Well.... OK, so it DOES provide a structure, which is not a bad thing. In that sense it fulfills the basic part of the 4e SC, by defining a number and type of checks that will resolve the situation (or maybe not completely resolve it, I am not going to break out my RM books to read up on it all).
Part of the reason for this is that it is based around a setting => situation model: that is, it takes setting input (terrain, weather, general attitude of the population, etc) and feeds that into the likelihood of a random encounter with a setting-appropriate being (or beings). But it doesn't take PC goal into account at all. So, for instance, it doesn't differentiate between (say) Frodo and Sam hoping not to get discovered by the marching soldiers at the Black Gate and (say) Aragorn declaring himself to Emoer and his riders, announcing his lineage and thus establishing a firm alliance (beginning with the loan of horses).
So it can tell you whether or not Easterlings or Rohirrim (or Paynim nomads) turn up in the PCs vicinity, but doesn't tell us whether or not they spot the PCs, or look for them, or any of the things that are actually central to resolving the situation described in the OP.
I GMed RM for nearly 20 years - hundreds of sessions, thousands of hours. The system is not only "a bit less adaptable", it's virtually worthless. It's lack of utility begins with "variable" for spells and "this may be modified due to an unusual circumstance, or if there is a tracker in the pursuing group" and only grows from there.The RM system in question is probably a bit less adaptable to every situation.