# su apache ./script
This account is currently not available.
It's because in
/etc/passwd is set as a nologin user:
apache:x:81:81:added by portage for apache:/var/www:/sbin/nologin
returns the error message.
Simply speaking, su isn't compatible with /usr/sbin/nologin.
What you want to do, instead, is run the command under the given user using
$ sudo -u apache ./script