There's nothing in the article answering my questions though. Have undersea volcano activity displaced water raising ocean levels? How much? Have these amounts been included in climatologist studies of global warming?
"Archimedes". Really, just look it up. Hawaii, the Galapagos, and others - all made by undersea volcanoes. If you understand Archimedes' principle, then you can answer your own question by extrapolation. When you then see that the volume created, whilst seemingly large to an individual, is extremely small compared to the volume of the planet's surface water, you'll see that it's not really significant. Also, you have erosion and collapses and other things going on. Again, you are focussing on a simple, single aspect when it's a far more complex matter. As such, you are drawing demonstrably incorrect conclusions. It's great to ask questions, but you need to understand their context and look for reliable sources for answers (hint: look for the weight of evidence, not just the evidence that supports your idea).
If the weight of evidence shifts, so too will my understanding of the topic. Whether it be something in which I am far from an expert (climate change, plate tectonics, etc.), or areas in which I am expert, or experienced, or otherwise qualified.
I am a sceptic, which is why I favour the weight of evidence and not the special pleadings.