they totally exist! the degree to which you can be conflicted is infinite (story of my life) there are no boundaries. anomalies are the keys to understanding and to ignore them to try to keep a theory together is just dumb. it's even more fascinating how there *is* SOME overlap between any two MBTI-enneagram type which then combined can constitute a very characteristic, strong vibe. for example, an INTJ 7 would be mentally quick, creative, demanding, a great planner, possibly narcissistic, impatient and irresponsible, and stuck in one-upmanship. while i personally haven't come acrosss a person like this, at any rate sheldon cooper comes to mind.
Either the enneagram causes people to adapt to a certain enneagram types or MBTI causes people to adopt particular enneagram types. I doubt that these types exist. It could also be that part of the two systems overlap, I think the biggest overlap is in MBTI's introversion/extraversion dichotomy. All 8s should generally be extraverted, saying otherwise is a complete contradiction. An extraverted 5 is similarly impossible, extraverts spend energy, how could they be people that spend energy if their enneagram type is almost defined by not spending energy. I could see INTJ 7 work, but it would be very conflicting, the introversion would clash with 7s need to spend energy. EXTJ 2 would be plausible, but most likely to mistype and never realize it. Type 6 isn't necessarily introverted or extraverted, which is my reasoning behind it having very little specific correlation to MBTI types.