Thanks forA.J.Caines at halplant.com andtkevans at tkevans.com for their
quick responses. Here is the suggestion:

/var/tmp itself is needed for the OS, so you can't exclude it.

If you want to put the image in /var/tmp, simply create a subdirectory
and put it in there, excluding that subdirectory, ie.

# flarcreate -n "Solaris 9 Web Server Image" -R / -x /var/tmp/flash
/var/tmp/flash/S9-web.image

>root at ch0-s1 # flarcreate -n "Solaris 9 Web Server Image" \
> -R / \
> -x /var/tmp \
> /var/tmp/S9-web.image

...

> ERROR: File /var/tmp registred in package database - can not be
> excluded.

I was following the instruction from the blueprint book JumpStart
Technology, it seems this is a mistake in the original book.