Why not run a stateless Hashicorp Vault in production?
I think you're misunderstanding what is considered bad practice.

Running vault with an in memory backend and being able to spin it up and provision it is fine. What is Not Fine is seeding the secrets in Vault from an insecure source.

If you are just using Vault as a way to simplify operations, as opposed to a long term persistent state store - then go for it.

One caveat - if you use the capabilities in vault to rotate keys for other integrated services then if you lose your vault cluster then you have just lost the keys to those services, so hopefully anything accessed using a Vault managed, regularly rotated, key is also easy for you to reprovision