Gestational sac seen on the ultrasound (dated pregnancy 4 weeks 6 days) however hCG was only 32 miu a week later and then rose to 130 two days later. Does this sound like it could be a viable pregnancy?

Check it out. Ask your doctor. It can vary based on labs, but theses numbers seem low to me.
Probably not viable. Something doesn't add up. The earliest we should see a gestational sac is with an HCG level of about 1000, so nothing should have been seen in the uterus at the levels you have. The rise in the HCG is very good and could go along with a viable pregnancy that would only be a few days along at that level of hcg. Get another us in 10-12 days and see what that shows.