I think overall we have very advanced technology for deep sea mining and can do it with relative safety, once in awhile a mistake does occur and it causes a problem but they are a rarity, the majority of deep sea mining is conducted professionally and very safe fully with our current technology.
Yes, I think we have enough advanced technology to engage in deep sea mining safely, because technology is very advanced. Ecologists and marine biologists, along with engineers, have spent their entire lives dedicated to learning how to do this safely. They can handle this while taking proper precautions for safety and the environment.
I think that with all the technological advancements we have in terms of marine vehicles and tools, we definitely have enough to deep sea mine safely. Nothing will ever be truly safe in terms of such dangerous jobs. But the advancements we have make it more than suitable to start such a tactic.
The technologies used to simply extract minerals from deep sea environments are not in themselves terribly complex - the trouble, of course, is determining whether these technologies can be used in ways that are not just economically-viable, but are safe ecologically. The deep sea floor is still one of the least-known parts of the Earth, and the effects of the inchoate deep sea mining industry are still less-known; however, there are justifiable concerns about heightened water toxicity in deep sea environments and about sediment plumes in mid- and deep-sea environments. Until technologies have developed to an extent sufficient to counter these problems, it would be irresponsible to say that the deep-sea's mineral resources - rich though they are - should now be exploited.
We do not have the technology to engage in deep sea mining as of right now. And even if we did, I do not think it is something we should be doing. We can't even drill oceanic oil correctly without destroying everything. If we start mining, who knows what would happen.