I just wanted to say that I/we have DID, and we have been able to type several of us, pretty accurately, with the Myers Briggs system (or at least, a simplified online version of it.) The trick is to have each part/alter take the test individually, and answer the questions only for their own self. In other words, imagine how YOU would answer the questions if you were the only person in your body. I know this may be difficult to imagine at times, but if you try to answer it for all of you at once, it will fail every time. That is because the "whole" you is only an illusion that is created by the combination of all of the individual "you"s. You are correct in saying that integration, in terms of merging all of the identities into one whole identity, is not always the best option. We tried that for nine long, torturous years, and it never worked. But now that we are learning to work together and not being concerned about merging, we find that we are making a lot more real progress.
Yes, it is true that personality type tests are more geared toward "normal" people who do not have any mental disorders. But if you keep that in mind when taking the test, and focus on the individual "you" that is out in the body at the moment, you will find that you can type your selves pretty accurately, usually. You will also find that it opens up a whole new world of being able to understand your selves better, and being able to find new and exciting ways to work together and help each other.
I hope you will find this to be as helpful as we have.
Take care!
Leyna Vincent (INFJ) of the Doug Vincent system