well, for me SOA!=webservice, per definition, it is 'services', but that is my opinion.
A is possible, but you loose transactional behaviour, unless you implement ws-transactions or something.
B is possible to, just embed it in each application and share the database
C: make an ejb3 wrapper for the commands
D: use the 'rest' inteterface of jBPM
I'd go for B