I could be wrong, since I'm a new zabbix user. But for me it seems like that Zabbix is based on the consept of Monitor alerts (Items & triggers) and have no functionality for stateless alerts?. I would like to see "raw" alert functionality in Zabbix, that makes me able to send stateless alerts to zabbix. If we compare Zabbix to HP Openview Operations Manager (HPOM) I would say that the functionality that is in zabbix_sender can be compared to HPOM's "opcmon". But zabbix have no functionality that could be equal to HPOM's "opcmsg" ?? Logfileparsing is one of several examples when raw stateless alarms is usefull.

opcmsg [ -help ] [ -id ]

application=application
object=object
msg_text=msg_text
[ severity=severity ]
[ msg_grp=msg_grp ]
[ node=node ]
[ service_id=service_id ]
[ -option variable=value ]*

HPOM is using a consept based on Message Keys. With use of templates/policy's it's possible to acknowledge "stateless alerts".

Zabbix is good, but have a few things to learn from tools like HP Operations Manager