I've made an “SNMP-MMonit gateway” which is a snmptrapd and a sender script. The script evaluates the trap, constructs the XML and sends it to MMonit by curl, but the XML is not 100%.
Unfortunately I haven’t find an XSD or an any documentation from Collector API, only an old mail on mailing list from Jan-Henrik Haukeland to plan to open the collector.
Are you still planning to open it? And if so, when?