viper-insert-state-mode-list

viper-insert-state-mode-list is a variable defined in `viper.el'.
Its value is

(internal-ange-ftp-mode comint-mode gud-mode inferior-emacs-lisp-mode erc-mode eshell-mode shell-mode)

Documentation:
A list of major modes that should come up in Vi Insert state.

You can customize this variable.