vertica/postgres copy text to binary column
As you asked for it: here is a Postgres solution if you can upload all the files to the Postgres server (or at least a directory accessible from there).

do
$$
declare 
  l_rec record;
  l_data bytea;
  -- change this to the server directory where all XML files are stored
  l_dir text := '/data/import';
  l_fname text;
begin
  for l_rec in select * from pg_ls_dir(l_dir) as t(name) loop
    l_fname := l_dir ||'/'||l_rec.name;
    l_data := pg_read_binary_file(l_fname);

    insert into the_table (the_xml_column) 
    values (l_data);
  end loop;
end;
$$


This must be run as the superuser (postgres)  because the functions pg_ls_dir() and pg_read_binary_file() have restricted access (for security reasons)