Sciatica can have a few different causes. More commonly, the nerve is being pinched by the periformus (sp?). In some cases it is a spinal issue.
In my case the issue was spinal. Core work did help a lot, but ultimately I needed minor surgery to really knock it down.
Either way, stretching the periformis or strengthening your core is probably a good thing, but you really ought to find out what the root cause is from a doctor. It took a couple MRIs to diagnose my issue.