Dylan,
The first thing to remember is that to use a 580 on camera as a master to control a 430 off camera is that the the 430/slave (the front) must be able to see the pre-flash from the 580/master so it knows what to do and when to fire.
Having the 430 behind an umbrella may be enough for this to not work, particularly if bouncing the master. You may find that you will need to put you slave on the stand backwards and then rotate the head 180 degress to fire through the umbrella.

Having said that you may find you don't have too many problems inside where the ceiling and walls will aid by bouncing the pre flash from the master to the slave somewhat.

Would you disable the on camera master or bounce it - I think that is going to be dependant on what effect you are looking for.