Had a look on http://www.pfa.net.au/index.php?id=191 at the CBA. Seems
to indicate that injury replacements DO count as a foreign spot (if they
are foreigners..). I would trust this over Wiki
In particular section 12 deals with replacement players. 12.5 e & f.
(e) The club must continue to comply with its obligations under causes 6 and 7 regarding roster size and composition; and
(f) the Club is deemed not to be in breach of the maximum roster requirement under clause 6.
clauses 6 and 7 discuss the rules of club rosters (minimum 20 players, max 23, 3 youth...etc)
Yep so an injury replacement can be an import only if he's replacing an import, or if the club has a spare import slot on it's roster.
So in our case Smith counts as the 5th import as he's not replacing another import.