Breast milk digests more quickly than formula, so it can help reduce the pain associated with reflux because there's less milk sitting in their tummy regurgitating back up into their oesophagus. Most of the websites I found reflux information on recommended continuing to breastfeed reflux babies for this reason.

My babe was a combination of exclusively breastfed (5 weeks), combination breast/formula fed (3 months), and exclusively formula-fed (from 4mo until now). His reflux started out 'silent' ie there was no vomiting, but lots of screaming, arching, breast refusal etc. It progressed to regular reflux, where he was vomiting 8-10 times after every feed. The vomiting didn't stop until a couple of months ago when I switched him to soy formula. For him, it didn't seem to matter whether it was breastmilk or formula - it still hurt!