Glitching Gameplay?

Is it allowed to glitch into the bank of Stormwind and kill the NPCs?

I mean, Alliance can always use the Ironforge bank so those many annoying horde rogues are doing useless kills.

But i want to know if is it allowed to glitch into zones on the "legit way" to disrupt gameplay?

Yes, it is allowed as long as it doesn't go to extremes. For example, if someone kills NPCs 24/7 and makes them unusable for days, that would count as disrupting gameplay. However, killing NPCs several times is fine.