Since metal views removes the ember script tags(metamorph tags), the content should be crawlable by search engines. Is that a correct assumption ? Do I still need to use server rendered HTML in tags ?
For SEO purposes it is still necessary to render some form of your content as plain HTML so that pages are crawlable.
The Ember.js core devs are currently working on the FastBoot project that is aimed specifically at solving this issue. You can read more about that here: http://emberjs.com/blog/2014/12/22/inside-fastboot-the-road-to-server-side-rendering.html