Did you already have a look at the respective Wiki pages at
Did you check that neither the machine where JBoss is on, nor the receiver (or any machine in between) has firewall rules to drop the snmp packets?
I used to send traps to receiver on a local machine just fine in the past.
How exactly did you specify the receiver in the managers.xml file? If you provided a hostname, are you sure that this correctly resolves to a ip address? Can you ping that machine?