Same brains can not be mindful and dissociate at the same time, if I understood it correctly. Here's a link to van der Kolk's lecture about childhood trauma, where he shows pictures of brains that dissociate.
https://youtu.be/zCwhE7m_Jd4?t=3090 It does not mean same parson could not do both, but at different times. And with DID, I'm not sure if we can do both at the same time too, because different parts use different parts of the brain, so can one be very dissociated while another one is not? I don't know, because I don't understand enough about what brains do then.
From personal experience I'd say I may do both at the same time, or that mindfulness practices makes me dissociate. Instead of getting aware of where I am while looking or touching things around me, I start to become part of those things. So the feeling of not being fully aware of who I am doesn't go away, but brains do get an answer, you are what's around you (if that's what I start to concentrating into). Another part of me stays in here and is able to look normal, while another part of me is totally out of realities and dissociating. Same thing with hypnosis, one goes deep, one is not affected. Same thing with using alcohol, one part gets drunk, one isn't affected but stays sober etc.
It can be a part who is not affected, but I don't feel presence or any switch there. Then it would be most likely Sami who stays aware always.
After year in therapy something has changed. Now I realize I have avoided all physical feelings before. I didn't wanna feel my body. Now I do things where I feel it, when I'm feeling well. This may be also some part, I'd guess Lucas in that case, who makes feeling the body not uncomfortable. He exercises and likes to feel it in the muscles, I don't if he's not there altering my experience. That is for sure him. But then there's other things, like that I went to hot sauna and pool with cold water in it in swimming hall. Both things I avoided before, I would not have done them, because they feel uncomfortable. Mostly I wanna be comfortable, because then there's not really anything to feel. But now I can get boost from doing something that feels uncomfortable for a moment. The good feeling comes afterwards, and partly from the fact I did it, like I was able to do something avoidable, survived from it, and feel good about myself.
If I think about yoga or anything where you have to concentrate on your body with thinking about it actively same time when doing it, I don't know.. well I DO know I don't wanna do it. Initial reaction would be to give it to someone else, make a part do it for me. For some reason Fourteen although it would trigger him. It would make Lucas dissociate too. Sami doesn't do things like that. So we don't do it, there's no one who would benefit from it at the moment. But it can change at some point. And maybe trauma sensitive yoga or what ever it was called would be possible, or something that feels more like exercising and feeling your muscles, than more meditative yoga. But breathing certain way and many of the typical positions of the body would make us dissociate easily.
I think it's complicated, the whole mindfulness thing. It's not suitable for our system, not the way it's presented usually. Not concentrating on our body, or the environment. I haven't actively tried different methods tho, since it's not something we do in therapy. And since it seems to be something that can change for us anyway, but hasn't yet. Relationship with the body has changed a lot without actively working with it.
I don't know if this helped, I don't have an answer to the question, but I do think it's complicated. And the answer you'd get with brain scan studies, or you need someone who understands how they work in brain, structural dissociation, dissociative state in general and mindfulness. However, if that's how it works for you, then I don't have any reasons to doubt it.