honestly ? I'm with a meh on this one.
It's really a situational scenario. TOO situational, to the point of being quite the achievement.
Not only do you need to be on THAT map, but you have to be on that team, at that position, summoning the last guy, who conveniently doesn't have a lace or cannot teleport or fly etc, while the objective is yet to be finished...

Personally? I see this as if u're a vaga, and the enemies got you stuck with a lace. Enemies can simply keep u stuck and go do the objective.
You cannot teleport out to stop them. So they ARE technically blocking you from finishing the objective because u're stuck when they could have simply killed u . The only reason they don't is to get more moolah from the bomb or hosties.
And u might argue that getting stuck with a lace is a game mechanic, but so is summoning people off edges, regardless of the map.

The fact that you can block this by having a lace should be sufficient, if it happened once? it's like those fucking idiots who use hell hunter and go off map with the bomb... and die there... shit happens, tough luck, you counter it or learn from it.
What would happen on crackhouse then if someone summoned u outside the map? or if u were shooting someone and they fell into the building cracks


I'll vote allowed for now, due to rareness of this "exploit".