Conducted By is NOT part of the artist name.
More than one main artist can be entered by adding another artist field.
When you add another artist field this way, you will see that another field is added beside the existing artist field, this is called the join field, and is for adding words or symbols that join the two artists together, for example 'Conducted By'.
The relevant guideline can be found here: http://www.discogs.com/help/database/submission-guidelines-release-artist#Artist_Fields
Please ask in the Help Forum if in doubt.