I do exactly this, use LiteLLM to bridge it. In fact I use LiteLLM to bridge OpenAI and Groq too. Even though OpenWebUI supports them directly, with LiteLLM I can control better which models I see. Otherwise my model list gets cluttered up. I configured this back when OpenWebUI only supported one OpenAI endpoint but I kept using it because it's just quite handy.

And no it doesn't cost extra credits, isn't ignored and doesn't have hardcoded context length. It works perfectly.