Hi, it seems like there's a lot of intercompatibility between different versions of the Sony RX100 housings. Are all UW housings for this camera compatible with all the different versions of the body (i->vii) or are there any notable housings or versions of the camera which are not compatible? TIA

It depends on the housing. The ones that fit the camera perfectly are not interchangeable. 
There is additionaly a significant design change starting with RX100 VI with respect to the lens, that makes it less usable for underwater photography. That’s why most dealer recommend the RX100 V(A). Here the movement of the front element of the lens is minimal and in wideangle position closest to the port