Is mid-May a good time to visit Mesa Verde and Shiprock areas?

That's a great time to go. Fewer people as most schools aren't out yet. And the weather is usually good. But you have to expect some snow.  Might not happen, but expect it.

The 4 corners has become more commercialized the second time we went, so expect that too.  Mesa Verde is a good stop.  They do have a few electrical sites in their campground.  But make reservations to be guaranteed one.