First of all, if you haven't done so already, you'll want to read the comprehensive OM-D thread and the comprehensive set-up instructions at these links:
Then in answer to your question . . .
Or really.. will I even use the 12-50mm underwater?
. . . lots of us do exactly that. I use mine almost exclusively as I like the combination of decent wide angle, zoom capability, and good macro functionality. It is certainly true that prime lenses and the ports to go with them will make technically better images in the appropriate circumstances, but when circumstances change or unexpected targets materialize you also can't change your objectives once you're under water like you can with the 12-50.