I've seen them refer to them upon need. I see signs that they are ongoing training. They seem to talk intelligently about what is happening in the database. What they say fits what I know. When there are problems, they seem to be able to troubleshoot them successfully. When application people want to learn more about how Oracle works, they happily recommend books that seem to have lots of good information.
OK, this applies to some of the DBAs. Some are obviously less competent than others, but the one that this project would be for fits the above description very well.
I lack the knowledge to tell more than that. It would take considerable effort for me to learn enough to really test whether they know what they are doing. I have other responsibilities.
I have read a couple of the books that they recommend though. And judging from what I learned there, they seem to be doing the kinds of things that they should be doing.
Beyond that, as long as I don't want to become a DBA myself, I have to assume. This assumption seems reasonable to me.
Cheers,
Ben