Reported in support ticket https://mynms.opennms.com/Ticket/Display.html?id=1557
The following message in output.log points straight to the problem:
==> output.log <==Aug 15, 2012 12:10:18 PM
com.sun.jersey.spi.container.ContainerResponse writeSEVERE: A message body
writer for Java class java.lang.Integer, and Java type int, and MIME media type
text/plain was not found
Changing the provider methods in RequisitionRestService to return a String rather than an int, and wrapping the return value in Integer.toString(int), resolves the problem. I'll commit the fix momentarily.