If you set your comps up without talking to the post house, you risk rendering everything over again. You may not have time to do that.
What flavour of HD is it? 720p? 1080i? What are the specs of their HD film? You need to match them.
You have a responsibility as a motion graphics specialist to deliver according to the proper technical specs as determined by the final output of the post house. Don’t let your boss prevent you from doing that.
Call the post house. If they’ve done HD before, they will have their own workflow, and will appreciate your asking them before you deliver, believe me.
Steve