I don't know of a specific report that will produce what you are requesting. I am unsure what you mean by "service account". However, I think you have a few options...

You could select all of your RHEL 5 systems, manage them in SSM and execute a remote-command against all them and compare the results. (the list of users in the '' will be fairly lengthy depending on your current environment). Then repeat for RHEL6.

# create your list of standard users (to ignore) using a vanilla /etc/passwd copied to /tmp/passwd
cat /tmp/passwd | awk -F: '{ print $1 }' | tr '\n' '|' | sed 's/|$//g'
cat /etc/passwd | awk -F: '{ print $1 }' | egrep -v 'list|of|users|from|last|command'

Or...

cat /etc/passwd | awk -F':' '{ if($3 >= 1000) print $0 }'

If this seems like something that might meet your needs, I can provide more detail how I use spacecmd for this type of activity. Hopefully someone else knows of a cleaner way ;-)