I'm looking into using zabbix_sender right now and ran into the problem that the "allowed hosts" field doesn't seem to verify the input. One can for example enter "fdksfsl" and zabbix will happily accept that value. Zabbix should return an error when it cannot parse the input.
Also one should be able to enter a subnet like e.g. 192.168.2.0/24 so that you can re-use the item on multiple systems without having to modify the allowed hosts for each individual system.