In the academic sense ("was it a design that influenced others?") I think the answer is yes. pg's essays about Arc and the language itself got a lot of people thinking about how to improve Lisp. Rich Hickey, creator of Clojure, was influenced to some extent by Arc.
In the practical sense ("is the community active and thriving?") I think the answer is no, so far. #arc on freenode is dead quiet and nearly empty, and there are only 20 new posts on arclanguage.org in the last 40 days. There's nothing wrong with that. It's just not "on fire", that's all. Not yet, anyway.
But it's only fair to give it time. pg said:
"Number one, expect change. Arc is still fluid and future releases are guaranteed to break all your code. It was mainly to aid the evolution of the language that we even released it."
So it's not surprising that an active, thriving community of library creators hasn't sprung up yet.