After some experimentation in the lab, I've come up with the following results. Those listed in the first block are the most vulnerable because a safe teleport can be performed from a deep blocked JIP, which is the easiest to learn and execute.
The second block of characters are immune to the JIP and their ease of performing a safe blocked JIK teleport is listed from easiest to hardest.
I should also add that the JIK hitboxes are also dependent on the stance of the character. Everyone listed had their chest facing the camera when I tested this. I haven't tested it with their backs facing the camera, so that has yet to be explored.
Reptile - Vulnerable to deep JIP, JIK hitbox is upper to mid thigh. Very forgiving and consistent hitbox.
Ermac - Vulnerable to deep JIP, JIK hitbox is upper to mid thigh. Forgiving and consistent hitbox.
Cyrax -Vulnerable to deep JIP, JIK hitbox is lower thigh. Forgiving and consistent hitbox.
Scorpion - Vulnerable to deep JIP, JIK hitbox is lower thigh. Forgiving and consistent hitbox.
Noob - Vulnerable to deep JIP, JIK hitbox is mid to lower thigh. Forgiving and consistent hitbox.
Baraka - Vulnerable to deep JIP, JIK hitbox is lower thigh. Forgiving and consistent hitbox.
Smoke - Vulnerable to deep JIP, JIK hitbox is lower thigh. Unforgiving but consistent hitbox.
Kano - Vulnerable to deep JIP, JIK hitbox is lower thigh. Unforgiving but consistent hitox.
Shang Tsung - Vulnerable to deep JIP, JIK hitbox is right above knee. Unforgiving but consistent hitbox.
Kabal - Vulnerable to deep JIP, JIK hitbox is lower thigh. Unforgiving but consistent hitbox.
Kenshi - Vulnerable to deep JIP, JIK hitbox is right above knee. Unforgiving but consistent hitbox.
Rain - Vulnerable to deep JIP, JIK hitbox is lower thigh. Unforgiving but consistent hitbox.
Sindel - Vulnerable to deep JIP, JIK hitbox is mid thigh. Very unforgiving hitbox.
Kitana - Vulerable to deep JIP, JIK hitbox is mid thigh. Very unforgiving hitbox.
Sektor - Vulnerable to deep JIP, JIK hitbox is lower thigh. Very unforgiving hitbox.
Raiden -Vulnerable to deep JIP, JIK hitbox is right above knee. JIK hitbox is too far out of Scorpion's reach to perform consecutively.
Quan-Chi - Vulnerable to deep JIP, JIK hitbox is mid to lower thigh. Unforgiving and seems random.
Skarlet - Vulnerable to deep JIP, JIK hitbox is lower thigh. Unforgiving and seems random.
Freddy - Immune to deep JIP, JIK hitbox is lower thigh. Forgiving and consistent hitbox.
Liu Kang - Immune to deep JIP, JIK hitbox is right above knee. Unforgiving but consistent hitbox.
Kung Lao - Immune to deep JIP, JIK hitbox is right above knee. Unforgiving but consistent hitbox.
Sub-Zero - Immune to deep JIP, JIK hitbox is right above knee. Unforgiving but consistent hitbox.
Mileena - Immune to deep JIP, JIK hitbox is lower thigh. Unforgiving but consistent hitbox
Nightwolf - Immune to deep JIP, JIK hitbox is lower thigh. Unforgiving but consistent hitbox
Sheeva - Immune to deep JIP, JIK hitbox is right above knee. Unforgiving but consistent hitbox.
Johnny Cage - Immune to deep JIP, JIK hitbox is lower thigh. Very unforgiving hitbox.
Stryker - Immune to deep JIP, JIK hitbox is lower thigh. Very unforgiving hitbox.
Cyber Sub-Zero - Immune to deep JIP, JIK hitbox is lower thigh. Unforgiving and seems random.
Jade - Immune to deep JIP, JIK hitbox is too random to be effective.
Sonya - Immune to deep JIP, JIK hitbox is too random to be effective.
Jax - Immune to deep JIP, JIK hitbox is too random to be effective.