Can a portable neonatal abdomen xray hurt a baby?

No. Radiation risk form x -rays is minimum, doctors will not order if it is not needed.
Just one? No. Many neonates have xrays. Unless they have very many, there is unlikely to be a harmful effect. But your question is timely: physicians have become more mindful of the cumulative radiation a person may be exposed to as our life expectancy rises. We should all consider the risk-reward ratio of any test or treatment we suggest.

Related Questions

Could a portable neonatal abdomen xray fulfill the requirement that the arrt wants for a pediatric abdomen?

Often, yes. I do not know what 'arrt' means, so I cannot address that specific issue. In the neonatal unit, almost all the abdominal x-rays are done portably. There are specific instances when one wuld need to transport the baby off the unit toget more high quality images or images with contrast such as an upper GI study or esophagram.