Should be OK . The following was on Google .... The EF-530 DG ST is an easy-to-use flash that provides a large amount of light, featuring a guide number of up to 53/m (174/ft) w/ISO 100. Compatible with AF single-lens reflex cameras of all popular manufacturers, this flash unit allows fully automatic photography with automatic TTL exposure control. In addition to the automatic mode, it also provides two power levels in manual mode: full and 1/16 power. This electronic flash combines a wide array of functions with ease of handling, and includes an Autozoom function that automatically sets the optimum illumination angle between 24mm and 105mm, as well as offering bounce and swivel capability.
So the Sigma can act as slave to the 580. However, if you get an E-TTL cable, you could control from your camera and use the 580 in a position other than on top of your camera, which is a lousy place to have light sent from
Hope this helps a bit, but I'm no expert, just learning a bit more myself. Look at Speedlite Forum, it can be very helpful.