In Terraforming Mars, do special tiles count as tiles you own when placing greenery tiles?
Yes.

Special tiles have your player marker on them, so they are your tiles, just like greenery or city tiles.

From the rules, page 5:


  Special tiles: Some cards allow you to place
  special tiles. Any function or placement
  restriction is described on the card. Place the
  tile, and place a player marker on it.


And


  Player markers: Each player uses his own color
  to mark TR, ownership of tiles, production
  (see page 6), and to indicate used blue card
  actions (see page 11).