Yes they can poke out of it.
Ask Detroit.
I staggered him with a cutter, then I proceeded to jump in punch, 1,1,2, Ex,cutter, and he managed to poke me out of it.
It's risky, so most people either forget there's a second swing of the ex cutter and get hit, stay blocking, or poke you out of it.
It does 11% chip, builds 55-65% meter back, and adds insane pressure.
I'll be looking into this further konqrr, but i've been using this tactic since early summer, and it's amazing.
As well as, F4, 1 cancel ex cutter, and only on jump in punch, 2,1,ex cutter, this confuses opponents pretty heavily.
When i finished tom off, that one didn't count. He could have punished me, but since he was so close to death, he stayed blocking the enitre time.
At 1:21, i started it after he was staggered.
It can be poked out of, I will further test this with detroit.