Last night I fixed the sed path and the data initialization issue (I was simply not copying the initialized data section to the .bin and .hex file, duh). I can verify many things using openocd and gdb on the development board, but when it comes to timers and interrupts it gets difficult. The same goes for anything that depends on input on the GPIO ports which of course are hooked up to different hardware on the real DSO.
So to get any further I think it will be needed to debug directly on a DSO. Maybe Jerry or someone at Seeed has everything set up for this? I haven’t opened my DSO and do not have my little screwdriver around, but from the schematics posted at code.google.com it seems like it has some kind of JTAG connector inside. But it will certainly not fit my JTAG adapter plug. Is there some pictures from inside the Nano v2 anywhere?
Of course, there can be just some small detail missing in my gcc setup, like those things I have discovered so far, but I am too blind to see my own mistakes 
In any case, I have learned a lot about arm debugging, and I can write up some short tutorials. I think the wiki will be a better place for this though, rather than having the information scattered around forum posts.