Anim dynamics specifically do not have anything but self collisions - so that docs bit seems incorrect. They used to check and correct for the character’s capsules / bounce against the underlying PHAT.
Other phat things can (depends on settings) respond to nearly all collisions.
Now a days instead of doing anymdynamics you would probably do a control rig solver to also provide some world interaction to things - like say a lara croft like pony tail for one.
It’s no longer just about anymdynamics really, if you consider that.
But even if it were, as I said, it used to collide against the main mesh PHAT asset as far as i remeber from the last time I set this us (before this topic was made).