I asked my vendor about the problem of creating a VLAN, and it turned out to be quite simple, once you know how to do it.
Here's a description showing how to create VLAN 2 with name "v2" using snmpset commands:
snmpset -v 2c -c private 192.168.123.254 .1.3.6.1.2.1.17.7.1.4.3.1.5.2 i 5
snmpset -v 2c -c private 192.168.123.254 .1.3.6.1.2.1.17.7.1.4.3.1.1.2 s v2
snmpset -v 2c -c private 192.168.123.254 .1.3.6.1.2.1.17.7.1.4.3.1.5.2 i 1