[Marttt]

try using a info_zombie_spawn entity.

{
"origin" "2466 -2191 -2"
"targetname" "tankspawn1"
"population" "Tank"
"offer_tank" "1"
"angles" "0 94 0"
"classname" "info_zombie_spawn"
"hammerid" "4744574"
}

To trigger just use something like "tankspawn1,SpawnZombie,,0,1"