They do (or did) have the thematic tutus and tanks - at least when we there in August 2012. I know this, because Baleigh and her friend insisted on owning one :) they purchased the Minnie Mouse one, but I recall clearly seeing a green/turquoise one that was decidedly little mermaidesque :)
The problem is, I recall they were quite hard to track down...I'll have to ask B if she remembers what store we saw them in. They were so much more comfy then the dresses (and trendy!).