I'm with Dave, I don't ever score the fat on briskets or butts. The amount of rub used on these shouldn't have any problem infusing its flavor into the meat.
I also do no not score anything. What I do score though is hams or picnics. Scoring these skin/rind on those does help flavor as well as enhance appearance. So much of the fat is gone after cooking a butt or brisket that I don't the scores would do much.