The answer to 'vacuum mildew' is that vacuuming mildew is generally not recommended, as it can spread mold spores and make the problem worse. Mildew is a type of mold that grows in damp, humid environments and requires a more thorough cleaning approach.
Instead of vacuuming, the best way to address mildew is to first identify and fix the source of moisture that's allowing the mold to grow. This may involve repairing leaks, improving ventilation, or using a dehumidifier. Then, the affected areas should be thoroughly cleaned using a solution of water and bleach or a commercial mold-killing product. For larger mildew infestations or if you have concerns about the extent of the problem, it's best to call in a professional mold remediation specialist.