If I send out Ad Hoc distributions of my App, is it possible for someone to hack the included files and get my code? I know it is compiled, but that Ad Hoc folder has a lot of stuff in it.
Yes. Anything is possible and vulnerable to being "hacked". It's up to you to put in the security considerations, such as encrypting your data and/or securing your connections.
In the end, if someone want's your data bad enough, there's not much you can do to stop them. It's really up to you to do everything you can to make it less easy to compromise your data.
In theory, they could de-compile your code.
But the reality is that de-compiled code is not very useful, and I'm not even sure there are any decompilers at the moment.
To help, you can make sure that ad-hoc builds do not ship with symbols included (by default I don't think Release distributions do). That would make it pretty hard to follow code even if decompiled...
Basically, I would not worry about that at all.