Regular drivers should be listed, whoever they are
Permissive use covers an occasional borrower. Somebody who drives your vehicles routinely as part of their work is a regular driver, and leaving them unlisted is the same misrepresentation it would be with a family member. Carriers rate who actually drives.
An employee driving is an employment question too
Where someone drives for you as part of paid work, an injury to them can be a workers compensation matter rather than an auto liability one, and harm they cause to others while working for you can attach to you in additional ways. Personal auto cover does not address the employment dimension.
Your limits travel with your vehicle
When anybody drives your car, your liability limit is what stands behind them, and your claims record absorbs the outcome. At this level of exposure that makes the underlying limits and the umbrella above them the practical protection rather than a formality.