since VMO/MMO exceedance is a precondition for an overspeed recovery, i suppose you're perfectly fine to use the speed brakes as part of the airbus standard procedure to recover from an overspeed condition. also VMO/MMO exceedance is not part of the speed brake inhibition logic. i assume airbus would have integrated this condition in the inhibition logic if it wasn't safe to use them during VMO/MMO exceedance.
i didn't find any limitation on the use of speed brakes in the limitation section of the FCOM (or maybe i'm just too tired already
).