Huh. I just scanned the manpage for Solaris 8 find and xargs, and they don't mention this. These arguments also give errors when I try them from the command-line:

bash-2.04$ uname -a
SunOS robotron.gpcc.itd.umich.edu 5.8 Generic_108528-18 sun4u sparc SU
+NW,UltraAX-e2
bash-2.04$ find . -print0
find: bad option -print0
find: path-list predicate-list
bash-2.04$ find . -print |xargs -P 4 echo
xargs: illegal option -- P
xargs: Usage: xargs: [-t] [-p] [-e[eofstr]] [-E eofstr] [-I replstr] [
+-i[replstr]] [-L #] [-l[#]] [-n # [-x]] [-s size] [cmd [args ...]]bas
+h-2.04$ 
bash-2.04$ find . -print |xargs -0 echo
xargs: illegal option -- 0
xargs: Usage: xargs: [-t] [-p] [-e[eofstr]] [-E eofstr] [-I replstr] [
+-i[replstr]] [-L #] [-l[#]] [-n # [-x]] [-s size] [cmd [args ...]]bas
+h-2.04$ 
bash-2.04$ which find
/usr/bin/find
bash-2.04$ which xargs
/usr/bin/xargs
[download]

Perhaps the GNU versions are provided in later versions of Solaris?