That is really odd. I wonder why they covered that up? It must not be totally unusable or they would've closed it completely. Hummmm. I wonder if the plastic vent is damaged behind that tape? That would explain it. Those deck vents just look like deck drains to me (i.e. French drain underneath). Maybe you can remove the covers and follow their path to some point. The pool vent (assuming overflow) might connect as well so that all excess water goes somewhere ideal.