Okay, I made some progress with the issue I guess :/
Installing NITDroid on a new extended ext3 formatted mmcblk0p5 partition stops the SDCard from being mounted in NITDroid, but installing it in /home, mmcbkl0p2 works perfectly. This problem happens in the 2.3.7 and ICS build.
Any light?
I'll try again to build the latest Gingerbread release from scratch and install it, let's see what happens.