I've never read or heard that mindfulness is contraindicated in DID, and I agree with you that it depends on the kind of mindfulness and the person's tolerance as to whether or not they can handle that particular exercise at that particular moment.
What I do is mindfulness meditation, with recorded guide. It's these:
http://marc.ucla.edu/mindful-meditationsAnd I usually do the "complete meditation instructions" because there is a lot of talking before the two silences, to remind me what I'm doing and why.
I started trying to do this daily about 3 1/2 years ago after I read that meditation actually changes the structure of the brain in a way that helps with emotional regulation, and even though I didn't know about the DID, I knew that it was very difficult for me to calm down after getting upset and that had made it very hard to cope with the stresses of therapy (as well as daily life!).
Before that I had gone to mindfulness retreats sometimes--6 hours of learning about mindfulness and practicing different kinds--mindful eating, walking meditations, etc. It was a nice break from the intensity and self-sacrifice of being home with 3 young children. I maybe went to 3 or 4 of those over the years. There was a calm accepting attitude among the people there, and a lot of reassurance about it being a learning process that could take a long time.
What I like about it is that it's about focusing on what's going on around me--really noticing and grounding, and then just coming back to the breath. Thoughts and emotions are just things to notice and observe rather than getting tangled up in them. The first time I started to cry while I was meditating and was able to just observe how it felt physically was kind of a breakthrough for me--I realized that I didn't have to just let the feeling take over and then be stuck in it.
So I guess it showed me that there could be a different way of dealing with feelings rather than dissociating away from them. I could survive a feeling, at least a small one, and then it would be over and I would still be sitting there, breathing.