This is actually more difficult to answer than you might think. There is something of a contradiction in the rules that both ICE and the RMC Team missed and therefore failed to address properly.
Section 10.5 Encumbrance does not, according to the way it is written affect anything but BMR.
The BMR is affected according to the modifier given on 10-10 Encumbrance Table, found in RMC Character Law, page 142 (RM2 Character & Campaign Law, page 15).
This modifier affects ONLY Base Movement Rate. And the note below it about Strength offsetting this penalty, and the penalty from armor also only applies to Base Movement Rate, I would have to say. This is because this entire section on Encumbrance talks ONLY about its effect on BMR, so the note would also only be talking about BMR.
However......
10-4 Static Action Table on RMC Campaign Law page 137 (RM2 Character & Campaign Law, page 45) has a section on it called "Maneuver*" and the asterisk says that modifications to maneuvers are made on the Movement & Maneuver table (i.e. this means the MM skills).
In this section there are modifiers for encumbrance that DO affect rolls on the Movement & Maneuver Table. There is another note that also explains this a little more and basically gives GMs the option to use the Section 10.5 Encumbrance rules for MM type skills as well.Personally, I believe that Encumbrance (one version or the other) should affect OB and MM skills as well as BMR (armor already affects DB, the question is.. should Encumbrance?)
In any case.....
The Official Ruling is
Encumbrance does affect MM skills as well as BMR
A GM just needs to decide which version...
(Note: if the GM is using Section 10.5 Encumbrance as the mods to MM skills, then I would also allow the strength bonus note to offset that penalty and the armor penalty)
Also note: It is my belief that the Armor mods (which are a type of encumbrance mod) are separate from the other Encumbrance mods because they can usually be dropped relatively quickly, but the armor is harder to remove quickly, and less likely to be removed during combat, thus separating them makes sense since it actual encumbrance can change quickly in such situations.