Green Lantern is very, very clearly a complete and utter ripoff of the Lensmen books. Was legal action ever taken over this? The title says lawsuit as the most obvious indicator, but I'm open to other actions as well.
Before he worked at DC,Julie Schwartz was an agent for many sci-fi authors, including one E.E. "Doc" Smith. Ray Palmer, secret identity of the silver-age Atom, was named after another Sci-Fi writer, Raymond A. Palmer. Julie deliberately made the new Silver-Age revamps of the characters more science-fiction in theme, as opposed to many of the golden-age heroes who had more magic-based powers.
The similarities between The Green Lantern Corps, a inter-galactic police force, using a super-weapon bestowed by a super-intelligent alien race, to the Lensmen, have never officially been admitted. But the hypothesis that Julie cobbled some somewhat generic concepts from his friend's work is not an unreasonable one.
Writer Mike Barr certainly thought so, when he added two new characters to the Corps in the classic mini-series Tales of the Green Lantern Corps. Arisia, a young female rookie Lantern, and Eddore of Tront were named for the good and evil super-races of the Lensmen series, respectively. A further reference is the fact that Eddore greatly resembles the descripion of Second-Stage Lensman Nadreck of Palain VII.
So was there a lawsuit? No. is there some DNA shared between the two? almost certainly.
Green Lantern isn't a rip off
Alan Scott appeared in 1940, First Lensman 1950.
The lens allows telepathy and enhanced senses. The ring allows flight, intangibility, creation of energy based objects but not telepathy or enhanced senses. The ring can speak the lens cannot.