In filing the Form 5307 and attachments to request a determination, a Form 2848 was filed with the tax matters specified as Form 5307 and related forms. This provided us with power of attorney. Now, can the power of attorney sign off on the certification for exemption from user fees on the Form 8717?

It sounds as if your language is general enough, but it's up to the IRS. Try it and if they don't like it, they will ask for a revised POA.

We have been told by the IRS that the 2848 must explicitly state [in the acts authorized section] that the power includes the specific power to execute the forms on behalf of the taxpayer.