Are there any characters in the SW universe that carry the last name Skywalker, and who aren't related to Anakin/Luke/Leia/etc.?
I.e., is the Skywalker name completely exclusive to the Vader lineage, or, are there others?
According to Wookieepedia, all known Skywalkers are descended from Shmi (at least genetically; there have also been multiple Skywalker clones in various media).
The Skywalker family was a Force-sensitive Human bloodline whose first known member was Shmi Skywalker.
This is not a directly canonical answer; however, the wiki is generally quite well maintained, and I doubt that an unrelated Skywalker would make it through without it being mentioned on the family's page.