If you're asking "why use DxH?" the main answer is its tight integration with Ektron. You can continue using your marketing automation system and it will share relevant data with Ektron. If you are instead looking to perform a wholesale migration away from a particular system, you can certainly do a one-time import of data into Ektron using the APIs. The difference there is that you would be moving away from the 3rd party system, whereas the DxH and its ContextBus allows both systems to work together.
You mentioned a webinar that you are following, so you may have already seen this, but there's a good webinar on the DxH here: http://www.ektron.com/Webinars/Details/Digital-Experience-Hub---Developer-Webinar/