I don’t know that it is stated anywhere. If you feel the docs could be improved you can always file a bug.
I believe so.
FWIW I have filed an internal bug with a suggestion to make an addition to this section of the nvcc manual to clarify that that is the only correct method to select the dialect of the host compiler from the nvcc command line. I cannot say if it will be incorporated or when. I won’t be able to respond to further questions about the status of that bug.