AFAIK it was not tested in a clustered environment. And IMO this would be very difficult and maybe impossible in the general case. But it should certainly doable on a process by process basis. Maybe Alex has more insights?
And once again.
Does jBPM BPEL work in a clustered environment? Does it support failover and automatic continuation of a process execution? How do timers and loops work in cluster environment?
I hope the answers are as simple as "yes/no".