Per the support request 01721859 which was opened on this same issue, the "send would block" is due to a known issue. If the configuration option umq_ulb_application_set_message_reassignment_timeout is set to 0, the "send would block" return can occur.
As for XML configurations, please see the following KBs:
KB 155788, "HOW TO: Convert a flat-file configuration file into the new XML configuration file structure in UM "
KB 149009, " HOW TO: Translate UM flat file configuration files into XML using example and script "
There is no special monitoring for ULB sources. At this time, there isn't any topic monitoring and the ULB characteristics and behaviors are on the topic level of Ultra Messaging. However, there are a number of source events which informs the application logic when specific ULB events occur. I believe these ULB events will provide the additional information that you are looking for.