So, is the oil leak contained?

[Tricky]

OK, so with this cap in place could they begin the process of pumping mud and/or concrete down the hole to permanently seal it?

And why seal it at all? I never got why they would dig an exploratory hole and then cap it to dig a production hole. What's wrong with an exploratory hole that it can't be used for production?

It's felt that too much of the upper hole is damaged and any attempt to produce from the original hole would be in danger of another breakage. However, the "relief wells" are not just for the purpose of stopping the flow, though they will, but also for getting production from the well.

However, not all wells are drilled to produce. Some wells are drilled only for the purpose of gathering information. This is especially true when the field is being evaluated. The non-producing evaluation wells might seem wasteful, but if they tell you how to best produce the field, they can save a lot of money in the long run.