There are only supposed to be seven "core" stories to be told and everything derives from them. I've never read Poul Anderson's stories but I doubt that Cameron plaguerized the guy either. Convergent ideas and stories crop up all the time. It's unfortunate that Cameron had to give Harlin Ellison money and credit for a similar idea. Harlin is the kind of guy who sues at the sniff of an idea similar to his and Cameron's was just close enough he sued for money and credit.
You may be right about those 7 "core" stories, but I didn't know there was an eighth one called Man in Wheelchair Uses Articial Lifeform to Get Around.