Should inmates while in federal prison file an income tax return?

IRS does not gives any different treatment. If the income is more than the filing requirement, you must file the tax return.

There is no income at this time, but the question arose because another person had stated that everyone should file a return as they will get money back. I am thinking that is wrong, if you don't have an income but thought I would check as I am not an expert.

If you do not have income you do not file. You must file only if your income is more than the filing requirement. Your U.S. Tax Return: 2009 Filing Requirements for Most Taxpayers