Yes, the human task service that is implemented as part of jBPM5 is based on the WS-HT specification, and that supports a lot of complex use cases about escalation, group assignment, delegation, etc.
Regarding a comparison with YAWL, that is mostly an academic effort, and is missing quite a lot of more advanced BPM features (the YAWL processes are rather low-level). And jBPM5 is using standards for everything (from process definitions using BPMN2 and human tasks using WS-HT to JPA/JTA for persistence/transactions, etc.) compared to the custom YAWL format, limited tooling, etc. At least, that is my (biased) opinion.
Kris