First of all the business-use case diagram is not really part of UML. It's more of a stereotype of the UML use case diagram.

Therefore, the "business actor" and the "worker" are both stereotypes of the actor in the UML use case diagram.

The "worker" represents the actual person within the organization being studied and who actually interacts with the use cases in the business use case model.

The "business actor" is someone external to the business who does not necessarily (but can) interact directly with the business use case but it surely impacted by the outcome.

EXAMPLE: In a storefront application, the sales associate would be the worker which interacts with the business use case while the "business actor" would be the customer which is indirectly impacted by the use case (i.e. receives a receipt, has their credit card charged, etc.)

Personally, I am not sure of the actual value this actor categorization makes in the day to day life of the analyst but it’s there and some folks use it.

Worker is an individual or group of individuals who have specific roles and responsibilities assigned to them within a project

Actor is a person(role)or external system that interacts with the system being modeled

Are there actually these two entities from a business modeling perspective? An actor is the one who performs any kind of work which directly or indirectly affects the system. A Primary Actor affects the system directly and a Secondary Actor has an indirect impact on the system. One could term the Business Worker as an end user which in effect is actually a Primary Actor.