NTA is for Netflow traffic only. If you're looking to send SNMP traps, that's where NPM comes in. As for the security of SNMP traps, if you're using SNMPv2c then making a secure community string using special characters and not leaving it the default "public" "private" is about as secure as you can get. If you're using SNMPv3 then you are using username/password for SNMP and it is as secure as you can make the password. SNMPv3 will be the most secure option, but can be difficult to configure initially and can be a maintenance headache with password expirations and changes.
Nothing secure is easy, and nothing easy is secure.