Under what license is the EAD DTD distributed here
( made available?

Is it in the public domain?

I'm interested in creating a Debian package for the DTD, to install a
local copy and register it with the Debian XML catalog system

If this Debian package is installed, and an EAD file is later validated,
then the local copy of the DTD should be used, rather than hitting the
LOC's web servers

Here's the Debian package I created,

I haven't completed the Debian "copyright" template because I'm not sure
how the DTD is licensed - here's the partially complete Debian
"copyright" template,