VSs show up in show-gateways-and-servers. Here's redacted output from one of my production managements:
[Expert@MySmartCenter]# mgmt_cli -f json -r true show gateways-and-servers limit 500 | jq -c '.objects[]|[.name,.type]'
["vs_a_a","CpmiVsClusterNetobj"]
["vs_a_b","CpmiVsClusterNetobj"]
["vs_a_c","CpmiVsClusterNetobj"]
["vs_a_d","CpmiVsClusterNetobj"]
["vs_a_e","CpmiVsClusterNetobj"]
["vs_a_f","CpmiVsClusterNetobj"]
["vs_a_g","CpmiVsClusterNetobj"]
["vs_a_h","CpmiVsClusterNetobj"]
["sw_a_a","CpmiVsClusterNetobj"]
["vs_a_i","CpmiVsClusterNetobj"]
["sw_a_b","CpmiVsClusterNetobj"]
["MySmartCenter","checkpoint-host"]
["vsxClusterA","CpmiVsxClusterNetobj"]
["vsxClusterAMember1","CpmiVsxClusterMember"]
["vsxClusterAMember2","CpmiVsxClusterMember"]
["sw_b_a","CpmiVsClusterNetobj"]
["vs_b_a","CpmiVsClusterNetobj"]
["vs_b_b","CpmiVsClusterNetobj"]
["vs_b_c","CpmiVsClusterNetobj"]
["vs_b_d","CpmiVsClusterNetobj"]
["vs_b_e","CpmiVsClusterNetobj"]
["vs_b_f","CpmiVsClusterNetobj"]
["vs_b_g","CpmiVsClusterNetobj"]
["MyLogServer","checkpoint-host"]
["vsxClusterB","CpmiVsxClusterNetobj"]
["vsxClusterBMember1","CpmiVsxClusterMember"]
["vsxClusterBMember2","CpmiVsxClusterMember"]
VSX cluster members (useful for things like version checks, syslog config, etc.) are type CpmiVsxClusterMember.
VSX clusters are type CpmiVsxClusterNetobj.
On a cluster, VSs themselves are type CpmiVsClusterNetobj (they are technically clusters, though you generally don't have to manage the members). I don't have any non-clustered VSX firewalls, so I don't know what object type a non-clustered VS would have. Maybe CpmiVsNetobj?