I have no idea about the chemicals involved in "ground eating", but couldn't you use a catalyst to speed up the reaction? And if the material that needs to be destroyed reacts with something naturally abundant, like oxygen, then just adding a small amount of catalyst for that reaction could be enough to do the job, since the catalyst will help many reactions complete before it is destroyed. Of course, there needs to be a known catalyst for that reaction in the first place.
But anyway, if you're eating through the ground, then why not just dig a tunnel instead? Have the guy with the cameyes watch for obstacles and then dig until you are under the vault. Then all you need to do is cut a hole quickly (since they are likely to have defences for that), either by using explosives or some sort of cutting torch or cutting laser. Or you can use chemichals for that last part, actually getting through the foundation and the floor of the bank.
Or for something really ambitious and dwarfy, you could dig under the bank's foundations, setting supports as you do so to keep it standing and then collapse the supports, causing the entire bank to sink into the ground. With all its inhabitants thoroughly rocked and/or killed and the entire bank underground, all you got to do is enter through a window and make your way to the vault. Or dig to it if sections of the building have collapsed (although I doubt it, given how armoured it seems). And since from the outside this will look like an accident (a sink-hole suddenly appearing or badly constructed foundation collapsing depending on how you do it) you won't have any police on your tail until they realize what's going on. And by that time, if everything has gone well, you'll be long gone.