If you are talking about the reset, you are crush countering with HP not HK.That shit is crazy sick, but I never crush counter with Roundhouse when they're standing. I doubt this works literally, but I'm digging the idea behind it. Let us know what you come up with bro!
If done right there is no gap between f.mk and s.hp, the only thing that should be punishable is the SPD but that can only be done with the Invincible reversal and possibly Birdie. Other characters normals shouldn't reach Gief.It's very situational. I think you can get a standing CC with HK on shoryukens, etc, just as they land, but I tend to use HP as it catches crouching opponents if I mistime it.
I would also refrain from doing the restand against characters with invincible reversals. You're rarely going to use f.mk without following up with a grab afterwards in neutral, so many opponents will (over time) react to it with a dp. It's not much damage, but it'll make you wish you went for the knock down and oki pressure. Against the rest of the cast I could see it being a solid option though, provided there is no gap between f.mk and s.hp for them to do a low attack or reliably armour.