Mutt
Yes it is used in the calculations. On the 744 for example using Flap25 and autobrake 2, 2reversers reduce the landing distance by about 200ft, 4 reversers by about 450 feet ( if my memory serves me correctly)
Using autobrake 3 the difference is about 40 ft and 90 ft.
Autobrake 4 and Max have no difference.