StackExchange apps and LaTex rendering
I doubt that there is one one and that there will be one in the (near) feature.

A look at stackwrap4j, the only Java Stackexchange Library that runs on Android, shows that the body (the content) of a post, which can be a question or an answer, is returned as plain String. The Tex equations are just included as plain Tex in that String and get rendered on the client side by the browser.

So, for example, Droidstack would need a Tex library that parses the tex code and returns a picture with the compiled tex. And I am not aware of such a library for Android.