No one 'owns' a client.
I took several from my old firm with me when I left. I knew I could service them much better as I was familiar with many tax credits for film and research which my previous firm would never dare to learn about them. I save hundreds of thousands for my clients annually. I'd think it would be an ethics violation not to poach, regardless of whether my old firm was up or down.
Sumwuns boss man has an issue of holding himself out as a CPA while suspended and feels necessary not to bother rectifying the issue. If **** hits the fan and he loses clients I would have no sympathy for him since he brought it on himself.