When Etsy says "service" it must result in a tangible item. Custom graphics services provide digital files of logos, banners, printables, etc. IMO a blog feature is not a tangible item.
This is from the Etsy Do's and Don'ts. You should contact Etsy directly to find out if a digital file with instructions on how to be featured on a blog is considered a tangible item.
Services
In general, services are not allowed to be listed on Etsy. There are a few exceptions noted below that are allowed as they produce a new, tangible, physical item.
Any service that does not yield a new, tangible, physical item is not allowed (for example: tailoring, restoring or repairing an item, photographic retouching or color correction).
Custom graphic design and digital pattern distribution are allowed; a digital file (for example: .pdf, .jpg, .doc) is considered the tangible, physical item.
An instructional crafting workshop is allowed as long as it provides the buyer with a tangible, physical item (for example: an instructional booklet, crafting supplies, a finished project that the student created in the workshop).