*** Information current for at least 1.3-Preview as built at 2005/06/15 ***

DFLY's inetd listens on all network interfaces and cannot be instructed
to bind on one (as does OpenBSD's inetd).  So while the manual says that
your /etc/inetd.conf entry should be:

127.0.0.1:8021 stream tcp nowait root /usr/libexec/ftp-proxy ftp-proxy

instead for DFLY it should be:

ftp-proxy stream tcp nowait root /usr/libexec/ftp-proxy ftp-proxy

and you should use /etc/hosts.allow to wrap/control access to ftp-proxy.
You must allow access to ftp-proxy from the networks that you expect to
use it.  This is somewhat different than what you expect if you have
used OpenBSD/pf/ftp-proxy where the redirection is done on 127.0.0.1.
So while the manual instructs:

rdr pass on $int_if proto tcp from any to any port 21 -> 127.0.0.1 port 8021

you should use:

rdr pass on $int_if proto tcp from any to any port 21 -> $int_if port 8021