Again, this breaks basic IP communication standards.
Packets like this would not traverse through any SPI firewall, or any NAT.
Even basic iptables firewall on your server would block such packets.
Any network device along the path that does any SPI or NAT will drop these packets.
These packets will be considered as unsolicited packets, since they are not responses to any established UDP stream (because of wrong IP header).
What you quoted from Juniper is for SNMP traps, which behave entirelly differently from RESPONSES to SNMP requests.
Imagine if NetXMS was to implement behaviour for every vendor's broken networking/snmp implementation...
That would be a very fast way to hell...
The correct way here is for the vendor of your device to fix the broken implementation, not for NetXMS to adjust to a broken implementation.
