A card isn't in play until it resolves.Playing a card is the process of bringing a card from your hand into play.
Cards that tap the site as an active condition require an untapped site as part of that active condition.
Cards that tap the site as an effect once they resolve require (by rule) an untapped site.
The both require the same thing, but for different reasons, and tap the site at different points.
The phrase "such an attack can occur only if one of the following criteria is met" seems to me to apply to any attack generated by a creature card.
Attacks generated by other sources (such as Dragons Ahunt) are considered hazard creature attacks, but are not generated by a hazard creature card.