DicomObjects 64bit Registration
As VS20xx is itself a 32 bit application, even though it is compiling a 64 bit application, which uses a 64 bit OCX, it cannot ITSELF access the 64 bit OCX for intellisense, #import etc. The standard requirements for using 64 bit COM component in VS20xx is that a 32 bit version with the same interfaces must be registered on the development machine (not of course needed for subsequent execution).
32 bit Registration
64 bit Registration
For deployment and distribution of your 64bit application, only DicomObjects 64 bit is needed.