Yes, swimming is really good for problematic spines. Also nordic walking. About 10 years ago, when I started nordic walking I remember I read a paper that concluded that nordic walking was superior to swimming in the management of back pains including sciatica, scoliosis, etc
Really everything that strengthens back muscles without putting too much pressure on them is advisable.
But running damages the lower back and can worsen sciatica since it involves jumping. Aerobics, step, anything that involves jumping can worsen sciatica.