There are a number of ways you could do this, but you need to know at least the basics of perl or another scripting language that you're allowed to run on the windows boxes.
Modify check_win_process.pl to search for those processes and error if it can't find them. If that perl script is already running, then there aren't any restrictions on whether it's able to do that or not.
If you're more comfortable with bash, see if you can make/modify a perl script on your windows box that grabs the process list and relays it back to nagios, then do bash stuff from there eg:
if "cat /tmp/proclist|grep oracle.exe|wc -l" -eq "3" ]
echo "oh no!"
exit 2
