No. Baldrick has a guide to adding subs. Adding another audio track follows the same process. I'd suggest following his method 2:
http://forum.videohelp.com/threads/277950-How-to-add-new-subtitles-to-an-existing-DVD
This should work with in-synch audio and subs if both sources have exactly the same framecount and content, and if there's bitrate to spare. If Muxman craps out during the authoring then you'll know it won't work.
In my opinion, unless it's for a child that can't read subtitles adding dubbed audio is lame.