Is the SD1M showing a RAW histogram in LCD quick-preview (ETTR) or jpg-based ?

Without actually knowing, I'd bet money that you're not seeing a RAW histogram--I don't think anyone in the industry does this right.

Presumably, you could switch the camera between RAW and JPEG modes, and see if the histogram changes.

I have a DP2M. I always overexpose by one stop, then underexpose in SPP by one stop, then export to TIFF. That seems to work well.