It would appear that the only way to accept invalid certificates is to go to the RestKit subproject, go to Build Settings > Preprocessor Macros and add the value _AFNETWORKING_ALLOW_INVALID_SSL_CERTIFICATES_ . You then need to clean your project.
I'm guessing that because the RestKit subproject contains AFNetworking some sort of pre-compilation is going on that cannot be reversed in your main project. So if you have the flag in the RestKit Build Settings, RestKit will compile with support for invalid certificates. Otherwise, by default, it will not.