The monkeys are a leftover from pre-Sirius Alliance experiments in bioengineering, specifically uplifting animals (in this case, chimps) to a full bipedal stance and near-human intelligence. The idea was to use them as footsoldiers against the Coalition (chimps are naturally tough and very strong, compared to humans), but the testing never reached final stages before the exodus.
Some scientist carried several cryo-frozen embryos with him/her on a sleeper ship, and eventually the experiments continued in one of the early colonies of Sirius. However, the matured 'test subjects' rebelled against their makers and manage to flee in one or more small freighters, and through luck or fate managed to find and survive the fickle jumpholes and dangers of the Omicrons, eventually finding and settling on a barely-habitable planet in what would eventually be known as the Omicron Kappa system. Being hardy and small in number, the chimps managed to survive, even flourish, on the harsh planet, until finally encountering a peaceful expedition of Zoners some hundreds of years later.
