By itself a block chain just stores hash with each block, they could be recomputed after a change. Just like how Git history can be changed.

Unless you're talking about a distributed public no-trust ledger, yes that can be solved with block chain as it's what Bitcoin is. But that's not a problem they're having.

> A blockchain could be used to enforce that immutability. Which might be an actual, useful application for blockchains.

Yes, and surprisingly the implementation is called Bitcoin ;)

Sure, but that’s only needed in a purely distributed environment. There is absolutely no need for a blockchain in a centralised private database you have full control over.