I'm not a tree or plant expert, but I do have many Arborvitae (can't stand looking at my neighbors house ) along my property line. I just leave the needle droppings. They don't seem to hurt the plant as mine are well over 20 years old and appear to be in great shape.
Remember that the dead once was live and it was made up of all the nutrients that the plant desires now. There isn't much better fertilizer than the plants own body. It will eventually decompose. For now it makes a great natural mulch.