Yes, but only for your troops.

The game leaves much for the players to discover/test.

When I rein a clan member and send my hero, do my boosts play out in the defense? The game is very unclear about this.

This ans is my observation that when we reinforce any player with our boosts on then that player dosent get bonus from us and its likely for every type of march you send weather it is an OS or Yielding or Attack/Defense...your hero applies only to your troops so does boosts do. First your troops and troops of reinforced town gets combined and both the states are calculated. Then when battle begins total of both of your troop's stats works against total states of enemy. And the one with 80% loss losses. That how it works in POP too as well as OS and in normal fights too.