Signing C++ Plugins For the Mac App Store

In porting Paint My Cat for the Mac App Store, I want our C++-based computer vision and AR tracking to work. And it does... right up until the moment I sign the app with codesign. At that moment, it stops loading our Plugin at runtime. (At least, I assume that's what happens, because I get a blank screen that looks very much like the call to that API failed completely and threw an exception.)

Can anyone explain what I need to do to get plugins working correctly with signed binaries?

OR

Is it the fact that my plugin accesses the camera? (Which I'm surprised at, because I'm signing it with the same entitlements file as the main app, which specifies use of the camera.)

I think this is a long shot for Unity Answers, but here's hoping.

Alex