The official word is this.
A. Refer to www.cisco.com/en/US/customer/products/prod_warranties_item09186a00800b5594.html
Compact Flash memory cards contain internal controllers. Typically vendors change these internal controllers without notifying/marking it on the outside, visible to the user. In internal engineering validation and field trials, Cisco has found that the quality of these components varies vastly, which in turn affects the life of the Compact Flash. Therefore, Cisco does not support third-party Compact Flash.
In addition, vendors approved by Cisco will provide failure analysis reports for failed Compact Flash units, which is not available for third-party Compact Flash.
That being said as long as you get a compact flash II card and make sure it is formatted correctly it will probably work. We once used a camera flash card to get us out of jamb and it worked. It's up to you if you choose to do this or not.
http://www.cisco.com/en/US/products/hw/switches/ps663/products_tech_note09186a00801a5d58.shtml