Although there are more powerful tools than Excel which a data scientist should know how to use, would it be expected that someone indicating they are a Data Scientist know how to use Excel?
It depends on the level of expertise that is required. Personally I know how to do most of the standard operations you would need for Excel but I don’t think a Data Scientist needs to know more than that.
If this is a job advert where they are asking for advanced knowledge of Excel as a Data Scientist and do not require much in the way of programming/machine learning skills then I would give the job a wide berth. It would indicate to me that the company putting the job out don’t understand what a Data Scientist is and are putting a job out to say they have one.
would it be expected that someone indicating they are a Data Scientist know how to use Excel?
A data scientist is someone who is better at programming than a statistician and better at statistics than a programmer.
Most data scientists use R or Python for data manipulation. And, most of the times they have to write production grade scripts where data processing has to be automatic, which are usually performed quite nicely by R or Python.
Excel can although be considered an added bonus with the candidate. IMHO, it should not be a criteria for selection and should also not be expected.