Speaking from experience working on the LX brand (the Linux emulation layer for Joyent SmartOS), we would not have gotten very far with our emulation layer if we did not also faithfully emulate quite a lot of /proc. For example:

    $ grep DESC /etc/lsb-release
    DISTRIB_DESCRIPTION="Ubuntu 14.04.3 LTS"
    $ uname -a
    Linux kappa 3.13.0 BrandZ virtual linux x86_64 x86_64 x86_64 GNU/Linux
    $ wc -l /proc/cpuinfo
    608 /proc/cpuinfo
    $ /native/usr/bin/uname -a
    SunOS kappa 5.11 joyent_20160204T173314Z i86pc i386 i86pc