Does your baby have reflux? It would be expected to find this bug in the gi tract, but it doesn't belong in the lungs. When this or other gi-specific bugs are found in the lungs, it can be a good idea to investigate the possibility of reflux, since that can cause problems with the lungs (aspiration, irritation to lung tissue causing inflammation, etc.) There are several meds that can help a great deal if that is the case.
Otherwise, you will often find 'mixed reviews' on this and many other bugs- some clinics treat them, others leave them alone unless they are causing obvious problems. We haven't cultured that one so can't offer personal experience. However, your team is very correct in that bugs DO often 'come back' after treating with antibiotics- more often, it's because the drugs don't really eradicate them, just beat down the numbers to a lower/undetectable level and they grow back over time. When our kids do get sick, they tend to need a longer course of antibiotics than a child w/o CF would need, but in order to avoid drug resistance, many drs will avoid treating these bugs when the child is doing well. That is the stance we take with what my child cultures.