No, Bolster Defense is only Bunkers and certain Units. Duckboards have very little affect in game besides being what the activates the Runner ability. Unless a Scenario says different, they aren't all that useful.
1)Do all duck boards grant bolster defense of -1 or just bunkers?
2) Do you add ALL the plugs values to the tank? For example with the hacksaw turret added to the Ostrich. Does the Ostrich now get 5,4,3,0,0 for the top flat grid attack and 2,4,4,0,0 for the bottom basic attack?
Yes. Plugs become part of the tank. If they add health or an attack, that gets added to the tank. It's not bolstering up their attacks, it acts as its own separate attack, but it is activated when you activate that unit for combat/movement. It can also target a different target unless otherwise stated. Plugs don't have their own separate health or movement unless otherwise stated. It's easier to remember that they just become apart of the unit.
Does the Ostrich now get 5,4,3,0,0 for the top flat grid attack and 2,4,4,0,0 for the bottom basic attack?
No. The Hacksaw Turret would be its own, separate attack with the stats listed on the card. The other two attacks stay the same. They are not bolstered by the plug.
Hope this helps.