In effect, it sounds like you want to sub-contract course design, or at least part of it. In theory, I don't see an ethical issue with this as long as nothing happens that will disadvantage the students taking the resulting course. The important issue is that the students get a high quality course, whether delivered by you or someone else or developed by you or someone else.
Of course it will be your responsibility to judge accurately whether the resulting course meets appropriate standards and to guarantee that it does when delivered. You are, in effect, taking on a management role in course development and are completely responsible for the result. But the process is less important than the result, IMO.
It will also be your responsibility to deliver the course in an appropriate (say, flexible) way. Students, as usual, need reinforcement and feedback no matter how the materials were developed.
I will note, I hope accurately, that courses delivered by Open University UK are (a) high quality and (b) developed by large teams, including, in many cases, the production facilities of BBC. The process is very involved and takes quite a bit of time, but the results are high quality. I suspect that other online courses have similar team development structures.
Normally it is good to acknowledge such help, but that can be a contractual issue and may need to be if it seems unwise to have students contacting the developer for any reason.
Sorry, but I can't help in finding such a developer.