Being that episode 4 features the Limiter, I am glad I held off looking into the possible connections between Iron Man and Ultraman. It turns out, there is no clear connection. Iron Man pre-dates Ultraman by about 3 years. The center beam on Iron Man was able to be used as a weapon in the early appearances. I looked real quick and it seems like the arc reactor was the power source in the original comics, just like in the movie, but the circle was just mostly there, it didn’t glow like Ultraman’s until the movie, I think. I was probably just thinking about the deign links between Neon Genesis Evangelion and Ultraman. Both feature invading-Kaiju fighting giants who have a 3 minute time limits. Iron Man sort of has a limit in the movies anyway, but it is easily dealt with for the most part. I still think the look of the Arc Reactor does feel like a nod to the limiter on Ultraman, but I don’t think there is enough evidence to say Granov intended that.
Below is some information I pulled together giving credit to the principal designers of Ultraman and Iron Man, as well as when they did that design work.
-Iron Man suit designed by Don Heck and Jack Kirby in 1963
-Adi Granov designed the Iron Man movie suit in 2008
-Ultraman suit designed by a collaboration between Eiji Tsubaraya (as I understand it, he is the primary creator of Ultraman), Kinjo and Tohl Narita in 1966
-Ultraman manga suit written by Eiichi Shimizu and drawn by Tomohiro Shimoguchi fame, but it is unclear who designed the armor in 2011