This script - lightly tested - will create a web-archive of each open web tab in NetNewsWire (always presupposing these are pages not protected by authentication):
tell application "NetNewsWire"
try
if number of tabs > 1 then
set the_urls to URLs of tabs
set the_titles to titles of tabs
repeat with k from 2 to count the_urls
set h_title to item k of the_titles
set h_URL to item k of the_urls
tell application "DEVONthink Pro"
set h_archive to create record with {name:h_title, type:html, URL:h_URL}
set data of h_archive to download web archive from h_URL
end tell
end repeat
end if
on error error_message number error_number
if the error_number is not -128 then
try
display alert "NetNewsWire" message error_message as warning
on error number error_number
if error_number is -1708 then display dialog error_message buttons {"OK"} default button 1
end try
end if
end try
end tell