The .rhosts file is read by the daemon (rshd or rlogind or sshd) at each login attempt. (Since ordinary users can edit their .rhosts file whenever they want, it wouldn't make sense to require root to restart the daemon.)
Make sure that the .rhosts file doesn't contain Windows line ending, and that it has proper permissions: it should not writable by anyone other than you (chmod 644 ~/.rhosts or chmod 600 ~/.rhosts). I don't remember whether the Tru64 implementation performs this check, but it's better to do it right anyway.
Also make sure that the file is a proper text file, with a newline at the end (all unix text files end with a newline, the newline is a line ending character and not a line separator). Make sure not to use Windows line endings, which would add an extra carriage return that unix doesn't treat as a newline.
Make sure that rshd isn't started with the -l flag, which would disable .rhosts processing.
The system logs on the server are where you'll find a clue as to what is happening. Tru64 keeps its logs under /var/adm by default (unless /etc/syslogd.conf has been modified).