Yes, it works exactly like this.

Just an example:
tor in its latest version wants adduser as a dependency. So one needed to install that even bb-power provided enough functionality to guarantee the correct working of tor (as in earlier versions).
So install fkdep-adduser and you may safely remove adduser without apt-get removing tor with adduser.

Mission accomplished.
Just make sure you have an alternative for what you want, here: bb-power providing adduser functionality (would need symlinking /usr/sbin/adduser again to busybox or reinstalling bb-power after removal). But that is easy peasy for people playing with such stuff, right?


--edit
this is valid only for 'unversioned' dependencies, see MentalistTraceur's detailed answer in next post!