You can definitely nurse in a ring sling or a wrap. It takes practice, but it can be done. If you go to the boards at thebabywearer.com you can find tons of tutorials and helpful advice.
I didn't clue in to babywearing until my oldest was 8 months old. He was definitely my fussiest child. DS2 and DD were worn in a sling or wrap or mei tai from birth, and they were SO much happier and relaxed. Having my hands free is a big bonus! Everybody has different ways to cope, but my imagination fails me when I try to imagine our lives without babywearing. DD is 11 months old and she has ridden in a stroller twice in her life. It's just so much easier (and less expensive!) not to have all this heavy equipment to lug around with her, you know?
To be clear, I totally count babywearing as holding the baby. :)