I understand that the way women dress in ballet dances would certainly be considered indecent exposure, or not tznius, but if the context is not meant to evoke lust but beauty, is the exposure of extra skin still ossur?
The Talmud (Avoda Zara 20a) prohibits intentionally gazing at any woman; even if the gazing is only in order to appreciate her beauty.
This is codified in the Ramabam (Issurei Bi'ah 21:2):
והמסתכל אפילו באצבע קטנה של אשה ונתכוון להנות כמי שנסתכל במקום התורף
Someone who gazes at even a woman's small finger, and intends to derive pleasure from it, is considered as if he had gazed at her genital area.
The same language is also codified in the Shulchan Aruch (EH 21:1).