On the one hand, this title accurately describes what's going on in the poem. This realistic description is important. Whatever else is happening on a symbolic level, this is a adventure about someone going diving. The poem has a lot to say about the basic details of that experience, like the equipment you need, the feeling of going under water, etc. So it makes sense that the title would be a simple description of the subject of the poem. Plus, it doesn't give too many clues about what else you might be looking for here.
In general, titles really set up the way you will read a poem, mostly just because they come first. It's almost putting on a pair of glasses. It can bring certain things into focus, or blur them, depending on the title that frames the work. Try this out: Imagine if this poem had been called "On the Vietnam War." You'd spend the whole poem thinking about how this related to war. It would be a really different experience.
Now that's not to say that this title doesn't give us anything to think about. The phrase "Diving into the Wreck" could mean a lot of things. In the poem it has a literal meaning, but it could refer to any experience where you plunge into a disaster, where things change suddenly for the worse. This title seems simple and calm, but there are strong currents underneath.