How to kill processes unresponsive to kill -9

It is possible that process is killed but waiting for parent to collect its return value. In that case after it is killed it would be in state 'Z' and not 'R'. In that case you should find ppid of process using ps command and kill the parent process too(If you are really sure it wont cause any problems).

The other case could be that for some reason process is restarting after being killed like tty. In that case the process id should change every time you do kill -9. See if process ID is changing every time you are try to kill it.

The process is waiting on some system resource, perhaps NFS? that is not allowing it to 'let go'. Would love to hear some solutions to this beyond mine...

reboot the box, or let the process sit around.

I wonder if you might be able to 'STOP' the process via kill -STOP {PID} to prevent it from consuming more cpu.

Restarting it should be possible even with another stopped process sitting around, but it may require a list port or shared memory segment that is still in use by the other process.