Yes, the 1DsMKII is exactly the same body as the 1DMKII. I have both and they can be used interchangeably in my Seacam 1DMKII housing.
Now, your next question requires a bit more explanation: "will a 1DsMKII (camera) fit in a Seacam 1Ds housing and work properly except the 3 buttons below the LCDs?".
1. The new housing has a much improved lever to accommodate the * button when using CF 4-1 (see below). All things considered, the second generation MKII housing is preferable. Whether you have a 1Ds or a MKII/1DsMKII, if you don't already have a housing, buy the MKII housing.
It is part of the new machining and can not be retrofit to an old housing. If I had to trade-off the buttons at the bottom of the LCD (when using a 1Ds camera) and the * functionality, I'd opt for the * and use the MKII housing.
2. For those with a 1Ds camera wanting to use the new MKII housing, it can easily be fit to that camera at the factory. Primarily it is the two forked levers at the top of the camera that need to be bent according to which camera is inserted.
3. For those with a 1Ds housing wishing to use the new 1DsMKII camera (which I assume is the point of your inquiry), we can fine tune it at our studio by replacing the forked levers and doing fine adjustments on a few other controls (on/off, main wheel). As there are small differences between each camera, we prefer to have your housing and camera. However, we can tune to one of my MKII cameras and it will very likely work with yours as well.
So, the short answer is for MKII/1DsMKII, assume they are identical.
1Ds is not identical to MKII but close enough to make it work. The thing we don't want to do is change the camera platform so we are always certain to maintain the exact optical center , just as it came from the factory. This is very precise positioning and wide angle performance requires it be unaltered.