Hola Jackie

In dictations, at the moment, we are using Peninsular voices. However, offering Latin American voices in dictations is one of our projects in the future. The reason behind having Peninsular voices only is simply technical. We do offer lots of content and voices that are Latin American in lots of our bilingual readers and also fill-in-the-gap exercises to maintain that necessary balance. 

With regards to the use of vosotros, if the particular exercise is more focused on Spain you may see the use of vosotros (the same way students are also seeing the more Latin American use of ustedes in other texts), however, students with focus Latin American Spanish are not tested on any conjugation of vosotros. 

Un saludo cordial