As of November 2022, you cannot find with google any declaration from the character designer Akiko Takase (高瀬亜貴子) nor novel writer Akatsuki Kana (暁佳奈) that proves that Violet Evergarden is inspired by Saber from Fate.
Since there is no declaration from the creators, we cannot answer,
"Did Violet Evergarden creators use Saber from Fate/stay as
As such, the general public and courts are limited to answer this question based on facts.
While not conclusive, this is a relevant fact to consider in light of the already obvious visual similarities:
The first work in the Fate/stay universe that includes Saber was
first published in January 30, 2004. The series went to create
a large universe in which Saber is a recurrent identifiable element.
By 2015, it had published well over 10 sequels or spin offs, and
over 4 animes showing Saber.
Violet Evergarden (light novel) was first published in December 25,
Therefore, Takase and Kana had at least 10 years to get wind of the successful Fate Series, and its flagship, Saber. It would be difficult to prove that they had no contact with any Saber visual content. This is even harder if you consider how artists/designers are advised to research existing works when trying to develop a new original work in order to avoid copyright infringement.
In the end, while there is no conclusive answer, the reality is that within Internet, too many people report finding similarities between Saber and Violet, making it so that popularly, they are identified as inspired on one another.
Lastly, please note that it is not only about visual similarities. Both Saber, Violet Evergarden, Alice Zuberg (from SAO Alicization) share a character archetype of: -blond noble knight- a heroine with a kind heart and the behaviour/mindset of a knight; wearing blond hair with bangs and western knight looking attire.