No but, Ruby makes it trivial. No decompilations, no assembly, no debuggers necessary. Drop into an irb in a running process, change stuff and get out in seconds
Compilation is not a security control. Also if you're handling transactions at a significant rate, PCI (with all its problems) makes sure there's a trace.
I'm not so sure. You can certainly attach a debugger to any running process. But that's not what parent was suggesting. He was saying anyone could attach a REPL. That's a totally different animal.
It's your own dumb fault if you expose the web-console or similar on production.