The distinction here is that "art" is either a specific work, or a collection of works, whereas "the arts" is a collection of collections. The Free Dictionary has a pretty good breakdown of the difference on their page for "the arts" — http://encyclopedia.thefreedictionary.com/the+arts.
A good summary is this definition: "imaginative, creative, and nonscientific branches of knowledge considered collectively, esp. as studied academically." Thus, if your job is not specifically developing the entire study of the fields of art, or, alternately, of a local community of artists and creatives ("the arts community"), I would not use the term "arts developer" in reference to yourself.
Additionally, I'd like to echo the concerns of the other answers. "Arts developer" means nothing to me, and I work in the software development field, in a largely context. What specifically do you do? There is likely a much clearer way of expressing it that skirts this issue entirely.