I'm an INTJ 9, but not many INTJs are. It's more likely for INTPs, but not by much: INTPs and Ti doms gravitate very strongly to being Type 5 Enneagram, perhaps the closest correlation between MBTI and Enneagram among all the various types. INTJs tend to be type 5, type 1, type 8 and type 6. The other types are rather rare.
The type 1 and type 8 INTJs will appear to be very "Te" or "TJ", being rather judgmental and confrontational. Type 6 INTJs will tend to be more "nice", but they don't give their trust easily. Type 5 INTJs are easily mistaken for INTPs, and vice-versa, as their personalities and reactive tendencies are very similar, even though their cognitive approaches differ.
I don't personally know of any type 2 or type 3 INTJs (though type 3 will be a common "fix" in an INTJ tritype). There are definitely some type 4 INTJs who are more emotionally introspective than the usual INTJ. I'm unaware of any type 7 INTJs, though I don't deny the possibility - type 7s tend to be very extroverted by nature, and extroverted perceivers by type, and that just doesn't fit the INTJ paradigm very well.
Type 9 INTJs will appear to be more in touch with their tertiary (Fi) and inferior (Se) than most INTJs (kind of like the type 4 INTJs). Like types 5 and 4, type 9 is a "withdrawn" type, naturally suitable to the introverted INTJ. The part that doesn't seem to mesh, at first glance, is that the 9 descriptions tend to be very "feely". All the Enneagram types are rather "emotional" in nature, but the type 9 is an archetype of gentle, peaceful emotions.
How could this jibe with being an INTJ? Simple: INTJs and Ni doms in general don't enjoy having turbulent thoughts and emotions in their heads. It stops them from thinking, and the natural state of the INTJ is to "think too much".
Being type 9 means knowing how to stay calm enough to think clearly all the time.
The danger is that type 9s generally stay that calm by completely ignoring their anger, so their anger can pop up unpredictably. Most of the time, however, they are calm and level-headed. Egging them into a fight will usually fail. A type 9 INTJ generally doesn't enjoy getting into long drawn out arguments where no one is listening to anyone else. They'll seem to be a bit more harsh than the usual 9, because for those matters that relate to their primary mode of understanding things (Ni and Te), they'll state harsh truths that have a risk of disturbing others' peace of mind, and they'll stand up for what they know to be true in this regard. In more personal/emotional matters, however, they are very gentle and accommodating - almost too much so ... allowing loved ones to get away with emotional abuse that others simply wouldn't endure. I've seen this born out in some (half-assed) statistics about which types were more commonly married than the average would indicate, and type 9s tend to put up with type 8's forcefulness and type 4's emotional dramatics more than other types do.
Want to know whether an INTJ is a 9? He/she is the INTJ who always appears to be calm, and no matter how much you try to troll 'em, they rarely take the bait. And when they do, they stay gentle and calm, even as they systematically come up with counterarguments to the troll.
