Hey, Good morning! Thank you for posting your question. Can you clarify what is meant by 'show z values'? Do you mean in the map or in the worksheet?
From your question, I can assume you mean you are using 'Add ArcGIS layer' when you said 'import service layer into Excel', if that is true, all the attribute data will be imported (showing Z values) but we do not support 2D/3D (z values) mapping in ArcGIS for Excel at this time.
Please let me know if I was able to answer your question or if you have any additional questions.
All the best,
Shannon
Shannon Cardoza
Product Engineer