[XeTeX] cmyk encoded files

[Daniel Greenhoe]

Print shops often require pdf files containing color to be encoded
using CMYK colorspace values.

Version 2.11 of the xcolor package says that cmyk is "supported by
Postscripts directly" (page 8). So if I simply specify
  \usepackage[cmyk]{xcolor}
in the preamble and compile with XeTeX/XeLaTeX, is that sufficient to
ensure the resulting pdf is cmyk encoded?

Secondly, is there any free utility available for checking the
colorspace encoding of pdf files (maybe similar to foolab's pdffonts
for checking embedded fonts).

Many thanks in advance,
Dan