If the developers want to introduce the likes of MongoDB, someone will have to support and maintain it. We don't know MongoDB, but I would happy to put time into learning it and until I get up to speed on it (or unless someone is hired to support it), it will remain *unsupported* or, at best, not well supported.
If that is OK with management, then it is not my problem. It is somebody else's.
This is one of those situations where both sides are a little correct and also a little wrong. The truth is somewhere in the middle. Backend staff don't have to face the business and tend to stick to the rules. Developers don't have to make sure things are running 24/7 so they come up with cowboy solutions that appear to work on their PC but will not scale. The solution off course is simple, we need to talk to each other. Easier said than done.
Philosophically, the inability of big organisations to move quickly leaves an opportunity for smaller more nimble organisations to fill in the gaps.