Vanilla stables say they increase the production speed of mounted units, but do not benefit keshiks, camel archers, chariot archers, Indian war elephants, and so on. Stables originally did so but this was broken when Firaxis changed their unit type. VEM fixes this bug by adding a "Mounted Archer" unit class, which the Stable increases the production speed of. However, it's not possible to link combat animations to new unit classes with our current modding tools.