Current Devonthink3’s Hook to New Script is to create a RTF record. You can modify it to create a group instead.
Here is a script you can used to replace the current New Item Script of Devonthink3 (Hookmark preferences window ->Scripts->Devonthink3->New Item):
Summary
tell application id "DNtp"
set newItem to create record with {name:"$title", type:group}
set refURL to reference URL of newItem
set itemPath to path of newItem
end tell
open location refURL
get refURL