Sorry, I don't understand the question - do you mean mapping a texture subresource to another texture array subresource? If so, then for mapping you just map the two subresources and then copy the data directly. With UpdateSubResource you more or less specify the locations in the parameter arguments and the function does the copying for you.
Map is used to map a complete subresource - for buffers that means the whole buffer, and for textures that can mean a lot of different things depending on the dimension, array size, and mip levels. UpdateSubResource has the ability to update only a portion of a subresource, which can be an advantage in some cases.
How do you map a subresource into a position in an array of another?
I'm probably not asking the right question... (and yes, sorry for the hijack)