Out of those, it appears that only Green Hills Integrity and VxWorks have any formal POSIX certification – http://get.posixcertified.ieee.org/register.html – and only the first is actually certified against the full 1003.1 standard, VxWorks is only certified for the PSE52 realtime subset
To "aim for POSIX compliance" without formal certification doesn't mean much, since to "aim for POSIX compliance" is compatible with supporting an arbitrary subset of the POSIX standard
To "aim for POSIX compliance" without formal certification doesn't mean much, since to "aim for POSIX compliance" is compatible with supporting an arbitrary subset of the POSIX standard