I served on a jury while being a JW when I was 22. I was told that it was a conscience matter. I decided to do it. No one gave my any problems over it. Fortunately, I was in a liberal congregation at the time, and the elders weren't so rigid. The congreagtion that I had been in a couple of years earlier would have tried to make the decision for me, and I would have been in trouble if I had served.
Maybe it depends on the personality of the elders/cong. as to whether or not it's acceptable.
Rita