If I buy the accessory screen room ( not the add-a-room, just the screen room) to be used with an extended leg awning will it be necessary to use the awning with the support poles in the traditional vertical position to secure the screen room?

You do not have to have the legs in the vertical position. Merely set the awning height appropriately and the screen room will attach normally. There are 3 stake down points on each side (middle and each corner) and one stake down point along the screen room front on one side of the door in a Shademaker screen room.