@Thorvald: In this particular case, I think so.
In My Honest Opinion...
Original Publication Date: January 15, 2020
... It’s okay to create characters one would consider “ship fodder,” but only in certain contexts.
Allow me to explain it for you. So, imagine you have a canon character who is entirely one-dimensional, has little personality traits, only appeared once in a franchise and the story he/she appears in is complete. You’re becoming interested in this guy, but the problem is, he/she doesn’t seem likable with the little background he/she has. This is why sometimes, you can imagine that outside of the story, they are probably dating someone, but that someone has never been spoken of and never will be because the creators have moved past that phase. This is where your creation comes in.
However, the creations you make would seem pretty lazily done if you only created them to fit that mold. You should still give them personality traits and a background. What is their life alone like? Do THEY have any relationships besides who you’re creating them for? The bio for this person/these people doesn’t have to be long and entirely detailed like a main character’s, but you still have to write them out like any other creation.
Here’s what I say to sum this all up: Writing out somebody to add depth to a shallow person who is one-dimensional and will never be seen again is okay to me as long as it’s done well, but writing out somebody for a well-developed person whose story is still incomplete for the sole purpose of shipping them/them having a sibling/etc. is not.
So basically, ship with purpose?