I've tried to install net-snmp both 5.06 and 5.0.8 and fund that snmptrap file is missed in /usr/bin - it seems that the ebuild somehow failed to install it there.
Created attachment 17213 [details, diff] net-snmp-5.0.8.ebuild.patch This patch of the ebuild seems to fix the problem. There file snmptrap was deleted by mistake by the ebuild.
Fixed in the latest net-snmp-5.0.9-r1. Please give it a try.