There’s an odd property with some anti airs. I think it has to do with the bounding box, which is separate from the character’s normal collision box that is used to keep characters from passing through each other. I’ve had matches where I’ve done EX RJ and at the same time the opponent did Dudley’s EX uppercut. The two of us didn’t hit each other until the very end of the attacks (RJ won). I think this is because the bounding box isn’t allowing the characters to get close enough for either of their attacks to hit. It is NOT invulnerability.
Against Seth: Against runaway players, use AJK to close the gap and get him into the corner. Neutral jump MP can hit him if he tries to escape off the wall. Just keep pressuring him with JKs, because the chip damage can really add up against Seth. Stay close, punish stupid things with cr.MP, and when you get a lead, watch out for anything desperate.
Against Dhalsim: I’ve been experimenting with Adon’s jump-in mindgames for this matchup. You can screw up his anti-air timing with AJK, and you can bluff an AJK with j.MP. The distance for the j.MP is what you want to use (to make it ambiguous), and then mix up your AJK timing, or just do nothing; you’ll be far away enough that his s.MP anti-air won’t hit you.