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You can hide a dash/surveillance cam. And you may be able to buy one that does not store the recorded video locally.
I'm a huge proponent of the use of vehicle dashcams, but everything in life has practical limitations and costs involved. It would be significantly less costly and likely more effective to take measures to secure the wing using theft-resistant fasteners than to set up surveillance hoping you get a clear enough view in the dark to give to police who may or may not choose to pursue the issue in order to catch someone after they make off with the stolen part.
OP, I hope you are able to recover from the loss. I'm sure you probably already submitted a police report and a claim to insurance. Some insurance companies won't cover aftermarket parts under comprehensive, but maybe yours does. Worth checking into.