Vertex AI has the same API as PaLM as far as I know. However, the authorization is through Google Cloud. So I use it like any other GCP API.
I love the idea of adding fine tuning as a node though. Here is the API for creating a model tuning job - https://cloud.google.com/vertex-ai/docs/generative-ai/models...
I wish I could use ChainForge nodes in Node Red.