If this were a linear circuit, I'd say the resistor helps to guard against thermal imbalance (current hogging). As the transistor gets hot and its beta increases, its C-E current will increase accordingly, resulting in more voltage drop across the emitter resistor in that leg of the bridge. The change in the transistor's bias point would tend to counteract the increase in beta.
However, since this is a (presumably) on-off bridge where the transistors won't be running in their linear regions anyway, I'm not sure what the resistors would be there for.
Resistors fail by opening the circuit, so the resistors may just be a simple fusing scheme.