I would imagine that the game's DB of information was designed in whatever version of C++ Markus uses. The DAT files that are not straight text files are compiled data files and the executable that Markus coded (OOTP#.exe) looks up information in these compiled data files based on the dat's files header info which holds the address in the dat file for each bit of data stored within. You can view these dat files (the non-text dat files) with any hex editor but since they are compiled files there is little you can do to edit them and the non-verbiage data will just look like strange ascii code. That's because it is compiled, and the same thing applies to viewing the OOTP#.exe file with a hex editor. The people that have written programs to capture the data from these files would most likely have asked Markus directly for the header information of whichever dat files they wanted to pull info from, and it's possible some of this required info is stored in the EXE as well.
About forum programmers not giving you this info: I doubt Markus would have provided them with this info if he thought they would give it away to anyone who asked - I am pretty sure he makes his living off this after all
. If you have programming skills and want to create a game add-on why not email Markus and explain what you would like to do - maybe he can help you out or at least explain things in better detail than I am able to.