Not any time. Your feedback loop must provide some direction so the iteration is at least heading towards an improvement. For novel applications you might not have a convenient way to do that yet.
Even with that provision there's still a possibility of incrementally updating output converging on a local maximum. That local maximum might not be a solution at all. If it is a solution then the model might still miss much better solutions that a real developer with more insight might find.
As you said yourself the models need external feedback if they don't have sufficient information to make adjustments by themselves. In some cases that feedback might be "Start again because you're hopelessly off track". Sometimes even when they start again they just get hopelessly off-track again. That can happen even if they are explicitly prompted to do something else. So even closely supervising the LLM and not using self-iterating agents isn't guaranteed to get good results for novel applications.
You're right though that in new territory you may often have domain experts who still cannot adequately define success in an automated fashion because this is literally something that hasn't been created before. So they must be a part of the loop. They cannot necessarily put into code and descriptions what "better" or "right" is for an LLM to follow. But they can recognize it when they see it. In this case, it's still best to create the tightest feedback loop you can. If the LLM is waiting 2 days for your feedback, the loop is 2 days long.
I would say that a system with some sort of binary evaluation that indicates whether it succeeded or not is receiving feedback. It could also be some kind of sliding scale - how close did it get?
Either of those might be useful for determining a good future direction to iterate in but that would surely depend on the nature of the problem and how it's possible to search for solutions. I'd still call it a feedback loop even if the evaluation wasn't enough to point in a specific direction for a further iteration though. YMMV.