OSX is basically BSD. Most of the concepts of cracking in unix or linux will apply. The debugger you will end up using is GDB. It takes some getting used to, but it is quite powerful for a user level debugger.

I believe antilove made a patch to add memmory searching to gdb. There is also a gdb config file more suited to cracking available. If you cant find these I will post them.

As far as LordPE and tools of the sort are only for Windows PE files. OSX uses ELF I believe. There aren't many packers made for unix. Some are upx, burneye, and shiva. These generally aren't used by commercial software. More commonly they are used to protect exploits.

Hope this helps.