No idea how many sets until Pirates, but he does make nasty combination with Renally and Alna. You pack your file with those two, and a heavy stack of grims - you see for Dub Rido to not help your opponent you need to kill 2+ units a turn. By having less units then he does the odds of Rub a Dub Rido hurting you are low, and since your front liner already has DF (Renally) the damage is often negligible.
Renally's power allows her to slap most units down in a heartbeat and using a Grim every turn or so also will knock a unit down, the occasional Rido Luck and wham bam you're slowly and steadily clearing the field. For the endgame finally you bring out Alna, who will be powered by a TON of grimoires you've already cast to be able to wack a mole anything that's left.
Another note about Dub Rido that I am sad to not see - he's an awesome late game SS. For 2 SP he can bring up the rear and guarantee *at least* 30 damage (not to shabby) but usually much more - because you see there is always a late game SP surge as your bigger units fall, and your file begins to dwindle in size. Except in special cases you will see around 90-130 damage coming from that awesome SS.
If you play a file that builds up SP early you can always run it as an early SS to take advantage of your build up and slap down anything you want that's potentially going to ruin your big play.
It's an SS that needs more use! An SS that has earned me victories many times!