The key to punishing the Jab DP is that you have to train yourself to not be Blocking. You have to learn how to play Bison without Blocking. Seriously. If you are Blocking when he Jab DPs and whiffs, you will be stuck for a brief period and cannot punish the Jab DP.
Instead, learn to be in Neutral or, better yet, holding Towards on the joystick and pressing Jab to stop yourself from moving forward. When I play against Kens, I know that once he gets close enough for Jab DPs to be a threat, he cannot throw Fireballs anymore (Standing Roundhouse trades with Fireballs on reaction. See if he keeps throwing Fireballs. ^_^). Then, when he starts whiffing Jab DPs, you are already moving forward (or in Jab delay but that’s not a problem at all) and you are free to kick him. Pretty much as soon as you see him DP, just walk up and Kick. Don’t worry about getting him on the way down. Naturally, you’ll Kick AFTER he stops hitting because it is so fast. Just go up and kick it. Again, if you are at Defensive Crouch or Holding Back, you will go into Block animation, then come out, and you can’t move forward fast enough to punish him.
Standing Roundhouse MAKES Bison good against Ken. Bison is one of the only characters Ken can’t whiff Jab DPs on mindlessly because of it. Once Ken starts getting worried and backs off to start playing Fireball games from afar, NOW go to charging down/back for Headstomps. But when he moves in, you seriously should never be charging up for a Special move ever. And without the Knee Bash traps, Bison has a way better chance of beating O.Ken than N.Ken.