I got this to work:
In a repeating command block:
/execute @e[type=snowball,tag=!standSummoned] ~ ~ ~ summon armor_stand ~ ~0.1 ~ {Marker:1,Small:1b,CustomName:snowballStand,NoGravity:1}
In a conditional chain command block:
/scoreboard players tag @e[type=snowball,tag=!standSummoned] add standSummoned
In a regular chain command block:
/execute @e[type=snowball,tag=standSummoned] ~ ~ ~ /teleport @e[name=snowballStand] ~ ~-0.1 ~
The Marker:1 tag gives it a really tiny hitbox, so offsetting it slightly is enough to keep it from getting in the snowball's way. Note that this summons the armor stand with its feet at the snowball, you might want to offset it farther down to get the effect you want.
Edit
I may have misunderstood the problem. Were you trying to get a projectile to kill an existing invulnerable armor stand on hit? If so, this is what you want:
/execute @e[type=arrow] ~ ~ ~ scoreboard players tag @e[type=armor_stand,name=targetedArmorStandName,r=3] remove vulnerable
/execute @e[type=arrow] ~ ~ ~ scoreboard players tag @e[type=armor_stand,name=targetedArmorStandName,r=2] add vulnerable
/entitydata @e[tag=vulnerable] {Invulnerable:0}
/entitydata @e[tag=!vulnerable,type=armor_stand,name=targetedArmorStandName] {Invulnerable:1}
The actual Problem is the opening { around ArmorItems:[]. Do away with that and it works.
/summon Zombie 195 202 2 {CustomName:"TheMiningTeam",ArmorItems:[{},{},{},{id:skull,Damage:3,Count:1,tag:{SkullOwner:TheMiningTeam}}]}
you're missing CustomNameVisible:1 to make the name always visible and not only when you're looking at the zombie (if you want that).
(you should probably use id:"minecraft:skull" instead)
Best Answer
I believe the problem is that your golden chestplate is in the leggings armor slot. Here is a working command that will summon a Zombie Pigman with a Gold Chestplate:
It is important that you list out the empty brackets inside of the "ArmorItems" tag, otherwise it will put the chestplate in the wrong spot.
I recommend mcstacker for easily making custom items, mobs, and other things as it makes it easier to not have to remember a bunch of NBT tags.