Well
Code:
initChatFrame(chatFrame, i)
is called only once for every active ChatFrame on PLAYER_LOGIN if thats what you asking.
As for
Code:
chatElement.Show = dummy
its just short for
Code:
_G[chatFrame .. i .. "Background"].Show = dummy
and i have no idea how often ChatFrameNBackground:Show() is called, but i believe it's at least once for every mousover.
Still from what i understand calling empty function shouldn't generate any garbage should it?