Bottom post of the previous page:
Monkeys not being able to see out of vents is a feature, apparently. Ventcrawling got changed a while back so that you need thermal or x-ray vision to see people while inside a vent, hence why xenos are unaffected.Monkeys need sufficient pressure and O2 to be able to survive in vents for long periods, scrubbers are almost always de-pressurised so crawling through them is a bad idea.
Also monkey fever forces you to revert to being a monkey even if you get made human via genetics or mutadone.