If you want to submit a digital 3D model, in some challenge (that you might conceivably win,) and propose to use someone else's labor, skill and effort, claimed as your own - why would you consider doing that?
Why would you do anything that you feel might be wrong, even if there is no "law" or "legal right" preventing it? There is a difference between "legal" and "moral." (Just ask college students who get in trouble for plagiarism. They were so accustomed to being able to copy stuff, wholesale, from the internet, while in high-school, that they can't conceive of why it's wrong in higher academia.)
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Now, if you were truly able to reproduce the work, having the skills and geometric understanding to do so, then that's different. It would honestly be your own work. Even then, attribution of prior work & inspiration is always appreciated (and sometimes required -- for example, with patent applications.)
I don't intend to scold, considering that I have may misinterpreted your meaning (my apologies, if so.) I simply can not understand why this question comes up so often.
Use your moral compass (internal or external) to guide your actions. If you are accountable only to man, then use man-made "legal" guidance. If you feel that you have accountability, higher than man, use "moral/ethical" reasoning.
Conditionally apologetic,
-Taff