Why would it make sense to genetically alter the facility's laboratory rodents to neuter them, merely to make them "easier to control"? Lab workers have been handling intact rodent test animals for many decades without a problem, and white rats have already been selectively bred for docility and friendliness towards humans. Not only does eliminating the rats' reproductive organs mean that the researchers can't track a treatment's effects on courtship behavior, fertility, gestation, or subsequent generations, but it also means that they can't legitimately compare their own results to any other research that's previously been conducted upon normal Rattus norvegicus. Plus, a lab that large and isolated ought to be breeding its own laboratory rodents to avoid having to ship them in; it'd be far more efficient to raise intact specimens for most experimental purposes, then castrate some of the males if anyone's project specifically requires infertile ones.
It doesn't make sense. You know more about it than the writers do. They just put it in because it seemed neat and creepy without really thinking about or researching it.
It may have more to do with not wanting to animate rat genitalia. That's what I assumed when I first heard that bit of silliness.