There is no reason why an employer cannot say something negative - as long as they can stand over it or as long as it is not misleading for example if you said someone was late every morning but omitted the fact that they always worked late to make up the time. The reality in Ireland is that most employers do not say anything negative or they use silence to communicate the negative things.
On the original question, the FOI applies to the public sector only. Data protection applies in the private sector and the arguement about an employees access to references is somewhat unresolved, see mmclo's reply above, the data protection commissioner seems to be of the opinion that employees should get access to references, even when they are given in confidence.