No "ignorance" at all, Bobby - the idea of "choreographing" The Song Of The Earth strikes me as utterly appalling, and I'm sure very few people would ever have believed it would work in this format. All it needs is Catherine Jenkins and Russell Watson as the pair of soloists to "complete" the "concept". However, ballet artistes display some of the most questionable taste imaginable when it comes to plundering the musical repertoire for background tracks, so I'm not really surprised.
When works like this are done as the backing for ballets, then usually the vocal soloists are tucked into the orchestra pit, yes. I remember someone did a ballet version of R Strauss's "Four Last Songs" back when I worked at the Coli, and Bronwen Mills was positioned in the pit each night for the shows.