It is possible for an experienced working chef who has become covered in salt and pepper to be described as a "seasoned" professional in a tongue-in-cheek or humorous manner. However, in a more serious context, being covered in salt and pepper could be seen as a sign of carelessness or lack of attention to detail, which might not be considered characteristic of a seasoned professional.
The term "seasoned" when used to describe a professional typically refers to someone who has a lot of experience and is skilled in their field. It can also imply that they are knowledgeable and capable of handling various challenges or situations that may arise. While an experienced chef who has become covered in salt and pepper may still be skilled and knowledgeable, their carelessness or lack of attention to detail in that particular instance might not align with the typical connotations of the term "seasoned".