First, to answer your original question... as long as you keep your eyes open (and the weather cooperates), you'll get amazing views on the Großglockner.
Also, what is the "romantic road"? If you mean the German Romantic Road (Romantische Straße), it's one of about a hundred themed tourist routes (Ferienstraßen) that criss-cross the country. It's a series of roads running from Würzburg to Füssen and it passes by some of the most well-known (if not necessarily most unique) historically preserved towns in Germany, such as Rothenburg ob der Tauber, Dinkelsbühl, Nördlingen and Landsberg am Lech. The Romantic Road probably is the most well-known Ferienstraße outside the country, mainly because it's been promoted so heavily for decades, it has an easy and irresistable translation into English, and it provides a non-Autobahn driving route part of the way between Germany's two most popular tourist regions, the Mittelrhein and the Alps. There's a common misunderstanding that the road itself offers particularly special scenery. In reality, it's just a secondary rural route that's no more or less scenic than any other in that part of the country. The intention was to visit the towns themselves, not simply to drive it. It's too far out of the way of your proposed itinerary, so I wouldn't bother.
Is there a particular place you get on the Grossglockner road from the Dolomites? Is it better in one direction or the other, view wise? Perhaps someone who has driven the route can comment, but on a map, it looks like the easiest way to reach it from the Dolomites would be via E66 to Lienz to Heiligenblut. Because you're headed to Hallstatt next, this seems like the only logical route. I've driven from the Dolomite region to Innsbruck and on another trip, from Innsbruck to Zell am See (near the northern terminus of the Großglockner) and the scenery is, of course, stunning. But I doubt it would be that much more amazing to justify such a long detour.
