Well, I think that exposing a process its only useful to run that process from outside, it's not like you could edit the wsdl to add some new capabilities. So you cannot have a running process and at some moment ask for its status from another process calling the first one via web service.
For me, takes no sense to consume locally a web service, but maybe i am wrong or a i haven't understood you need.
I would connect database, and check for process status in bpo.BPAStatus table, with read only user.
If a better solution exists, I would like to know it too.
Regards