do you mean that Adobe DNG converter does not preserve the raw data read off sensor when it converts from IIQ to DNG ?
Yes, of that I'm 100% positive, that's easy to see. I don't think the DNG specification has support for the large amount of calibration data that IIQ packs (well, maybe with the most recent spec?), so the only possibility is to apply calibration data inside the converter and then save. Even if DNG format itself had/has support for calibration data few third-party DNG software would care to implement support for it as it would basically be only IIQ-converted files that would use it, so it's probably a good idea to keep the DNGs simple.
Actually, I think most other medium format CCD backs "cook" their data before writing to the file, like Hasselblad for example. Ie the back is individually measured in the factory and calibration data stored in the back, but calibration data is applied before writing the raw file, so you get a "cooked" raw (.3FR in the case of Hasselblad), just like the DNG in this case. Note that a CMOS sensor don't have the same need of calibration as a back based on a large CCD with multiple amplifiers for readout, so nearly all raw formats don't pack any calibration data at all.
From my perspective I'd prefer that the IIQ format had cooked data too, as it would make it a lot
easier to support, but for scientific use cooked raws is not great of course, so doing it the IIQ way has its merits. The file is pretty ugly before applying calibration data though, one quadrant can have as much as 0.1 stop of more amplification than another etc. Calibration data only fixes dead pixels/columns, amplification offsets, amplifier linearity and slight pixel sensitivity variations over the sensor surface (flatfield). Simple scalings to fix linearity issues (ie all flatfield stuff and amplifier scalings) I would not consider to be that controversial even for scientific use (it's reversible), removing of dead pixels/columns is perhaps more so. As far as I understand almost all CCD sensor of this large size have some permanently bad pixels, so it's something that needs to be done in some stage for every back.