Goldsworthy makes mention of Roman deserters in his book The Fall of Carthage. I cannot remember if he mentioned them fighting for the Carthaginians, but the return of deserters was an important part of the treaties for the 1st and 2nd war. When I get the chance I can read those chapters again, but I am pretty sure that during the 1st war there were Roman deserters fighting in Sicily for Carthage. Whether that was forced...