I think if they were ever going to fight Vader in a force duel, Vader would probably just overwhelm him. Dooku's lightning would just be deflected by barrier, and at best he'd probably just knock Vader back with TK. Dooku would be able to defend for a few secondsat first but Vader's sheer telekinetic might would just send him flying or shatter his barrier once he starts to weaken, realistically there isn't much he could do to Vader
If he had his Korriban amp, he'd die with a bit more of a fight