You are treating the results as a Bull Rush attempt (in terms of if/where to move the target), but you are not actually attempting to Bull Rush the opponent yourself. Feats such as Greater Bull Rush only impact an actual attempt to Bull Rush...
Greater Bull Rush:
You receive a +2 bonus on checks made to bull rush a foe. This bonus stacks with the bonus granted by Improved Bull Rush. Whenever you bull rush an opponent, his movement provokes attacks of opportunity from all of your allies (but not you).
Improved Bull Rush:
You do not provoke an attack of opportunity when performing a bull rush combat maneuver. In addition, you receive a +2 bonus on checks made to bull rush a foe. You also receive a +2 bonus to your Combat Maneuver Defense whenever an opponent tries to bull rush you.
Emphasis added to both quotes--These feats clearly only apply to actual Bull Rush attempts. Using Wind Blast isn't Bull Rushing, it is using Wind Blast, which happens to use the Bull Rush rules to determine results. The same would apply to any other ability that is not a Bull Rush but emulates the results of Bull Rush.
Logically, this makes sense. The feats mean you have a greater ability to actually Bull Rush someone. This implies strength, reflexes, knowing how to get proper leverage and drive with your legs, etc. Using a magical (or other) ability that also can push an opponent back one or more squares requires magical ability, not any of these physical skills.