Let's imagine a normal person. If they have been Imperiused and have enough will, they can resist and eventually break free of the Imperius Curse. So, put yourself in a Dark Wizard's shoes for once, and imagine, what prevents you from Imperiusing a person?
- Their will
- Their emotions
- Their care for themselves and others
For a Dark Wizard to be successfully be able to Imperiuse a person, all these lifelines have to be cut.
Will someone, even after being Kissed, remain alive in the first place?
When someone has been kissed by a dementor, their soul is sucked out. Irrespective of this, they will continue to exist as mentioned in the OP, but as 'an empty shell'.
"You can exist without your soul, you know, as long as your brain and heart are still working. But you'll have no sense of self any more, no
memory, no...anything. There's no chance at all of recovery. You
just - exist. As an empty shell. And your soul is gone
OK, but what are factors that make sure that I can still be Imperiused?
For once, you will -
- Not have any sense of your self (preventing you from resisting the Curse. Why will you fight for yourself, if you have no sense of your own 'self'?)
- Have no memory (preventing you to fight against the Imperius Curse for others, as you don't remember anything)
You have your organs intact, for one, and that includes your brain. Last time I checked, if you have a brain, you can be Imperiused.
Since there is minimal (or no, as I would argue,) resistance to the Imperius Curse, someone who has been Kissed will be easier to Imperiuse.
Also, to answer your main question,
Yes, someone who has been Kissed (and has enough organs left to live) can be Imperiused.