Yes, definitely cabin 6029 on the Summit is a Sweet 16. On all the Millennium class ships the first 8 balcony cabins on either side of deck 6 forward are twice the depth as the standard balconies.
Before our 2015 Summit cruise I used this thread to verify it, and you'll see a picture is worth a 1000 words.
Our travel agent at the time insisted there was no such thing (the deck plans don't show it), and even after sending her that link, I finally just stopped arguing and had her book 6035, 6030, and 6021 for us, our daughters, and son-in-law.
The only pics I took are attached. On the first one you can see how we had a nice clear view towards the aft of the ship because we stuck out (this was the repo from Bayonne to San Juan - so the Verrazano). In the next pic (it was my 60th bday and lots of gifts sent), you can somewhat see that the balcony was deep enough that we had loungers not regular chairs.
The first half of the balcony is covered by the balcony above, but the outside half sticks out. It's great for extra sun, but cruisers in the above balconies can look down.
The first 3 forward Sweet 16s on each side are encased in steel framing and DON'T get the full sun - they are a bit darker. But the first balcony - 6021 - was perfect for my redhead daughter who avoids sunbathing and wanted some quiet privacy and fresh air for studying for grad school. 6029 has the regular deep and open balcony.