Hi Brandai,
You can also assign to a specific user. Instead of <roles>, you can define a <user> tag:
1<user>
2 <email-address></email-address>
3 <screen-name></screen-name>
4 <user-id></user-id>
5</user>
You can choose one of these three attributes to identify an user.
Regarding your last question, Jbpm also supports mail notifications. You will find more informations @ jbpm docs.
Cheers