Probably you already got BBDB working with Gnus, but since this article appeared in my search results when I had the same issue, I thought I would post my findings here.
The answer here got things working for me: https://stackoverflow.com/questions/22174756/insert-current-entry-into-bbdb
Here is my bbdb configuration:
;; contact list
(use-package bbdb
:ensure t)
;;;;;;;;;;;;;;;;;;;;;;; bbdb config from https://stackoverflow.com/questions/22174756/insert-current-entry-into-bbdb ;;;;;;;;;;;;;;
(require 'bbdb)
;; initialization
(bbdb-initialize 'gnus 'message)
(bbdb-mua-auto-update-init 'gnus 'message)
;; size of the bbdb popup
(setq bbdb-pop-up-window-size 0.15)
(setq bbdb-mua-pop-up-window-size 0.15)
;; What do we do when invoking bbdb interactively
(setq bbdb-mua-update-interactive-p '(query . create))
;; Make sure we look at every address in a message and not only the
;; first one
(setq bbdb-message-all-addresses t)
;; use ; on a message to invoke bbdb interactively
(add-hook
'gnus-summary-mode-hook
(lambda ()
(define-key gnus-summary-mode-map (kbd ";") 'bbdb-mua-edit-field)))
(bbdb-initialize 'gnus 'message)
(add-hook 'gnus-startup-hook 'bbdb-insinuate-gnus)
(setq bbdb-user-mail-names
(regexp-opt '("david.miller@armedia.com"
"david.oc.miller@gmail.com"
"dmiller@davidocmiller.tech")))
(setq bbdb-complete-name-allow-cycling t)
;; no popup buffers
;;(setq bbdb-use-pop-up nil)
;;;;;;;;;;;;;;;;;;;;;;;;;;; end of bbdb integration ;;;;;;;;;;;;;;;;;;;;