I think he has spoken about his development methodology and codebase in interviews. From what I remember based on his description it would horrify any professional engineer who saw it but it seems to work for him.
This is the reason DF sprang to mind for me, too. From what I gather, tools like Dwarf Therapist work by directly manipulating the game's memory. If it were open source, I'm sure there would be some halfway sane plugin system by now.
Also, having the source code would mean that one could compile it for ARM devices...
Here is the AMA where he briefly touches on some of his implementations:https://www.reddit.com/r/IAmA/comments/1avszc/im_tarn_adams_...