IMO, it’s not going to hurt but I don’t see any benefit to the marinade and rub method. Or, to quote my granddad, “That's taking a long road to the little house.”
Marinades penetrate only about 1/4” so just the surface of the meat will be affected. Marinades can work great for thin steaks or on other meats that need a boost in the flavor department (skinless, boneless, tasteless, pointless chicken breasts, for example). But it won’t do anything for the flavor of the interior of a dense, thick muscle like brisket. By then adding a rub before smoking, you’re introducing yet another set of flavors that could conflict with those in the marinade. Or, some of the main ingredients in both your marinade and rub could combine and overpower all the others. Having your brisket may turn out too salty is probably the most likely result of that scenario.
Doing one or the other would be fine, but it seems to me that doing both could be counter-productive and probably more work than necessary.
Looking forward to hearing other’s thoughts.
Have a good weekend.
Ken
