Yes, it seems that they can do as long as the information they seek falls within the remit of their job as a councillor. My local council has clarified this in recent weeks after there was a complaint about a councillor doing just this. Although, I don't agree with it, I think you have to remember that County Councillors are paid a salary by the local authority to look after the interests of the community. My county councillors are on about £27000 a year plus expenses. In that respect, they have the same rights as other council employees and like it or not, council staff access data on a daily basis about individuals.
It strikes me that such behaviour might be beneficial for the community in the long-term. He might feel he needs to find out why people are leaving the area. It might be due to vandalism, anti-social behaviour etc and it's part of his job to try to put these matters right.
It's not an offence against the Data Protection Act as long as he doesn't misuse the information.