I dunno... I guess it all depends on your expectations and how you define success.
Under the right circumstances/conditions the NHL should be able to do
fine in Atlanta (or Houston, or Phoenix). When talking about markets with that kind of population and GDP an NHL team should be able to carve out a large enough niche to comfortably sustain itself, and if a franchise can do that, IMHO it qualifies as a success.
When talking about expansion to these large markets I know some folks like to talk about what kind of impact it will have on things like TV viewership/rights fees (big $!?) talent pool (prolific new pipelines!?), and just a general increase in relevance of the league/sport (ESPN will talk/yell more about hockey!?), and the answer to that I think, even in the long term, is very little... And that's fine?
For the most part I think people expecting or demanding those things are either enthusiastic supporters high on their own hopium, or critics in search of a metric that can used at some point in future to deem the market/team a failure.