Important part was Qt, Qt 4.8.x 64 bit is not exist, we should build 64 bit version of it. The trick to use Qt sources from DAZStudio4.5+ SDK\bin\x64 and mix it with headers from installed Qt 32 bit is a huge mistake that I did. it will fail to register the actions!
I'm happy that you got it to work, but you are still a bit confused and it might bite you in the future because your explanation of why it works doesn't make sense.
There are no sources in DAZStudio4.5+ SDK\bin\x64, only precompiled 64 bit DLLs. You do not have to, and should not, compile Qt at all. The build artifacts it would produce are already in the directory you cited.
There are no 32/64 bit headers in the Qt install. A header is a passive thing; The bitness is determined by the compiler when it compiles a compilation unit that #includes it.
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I'm happy that you got it to work, but you are still a bit confused and it might bite you in the future because your explanation of why it works doesn't make sense.
But, you got it to work, so you're in the club :)