Does this plugin work with Formidable Pro?

Not that I know of.
I only added Gravity Forms to automatically connect with it.

However, any plugin or code can easily use this Plugin, but you will need a developer or someone who knows php code to do it.

See the How to Use Section
http://wordpress.org/plugins/gravitate-encryption/other_notes/#How-to-Use

You can use this code to Encrypt and Decrypt any data:

if(class_exists('GDS_Encryption_Class'))
{
   echo GDS_Encryption_Class::encrypt('This is the Text to Encrypt');
}

if(class_exists('GDS_Encryption_Class'))
{
   echo GDS_Encryption_Class::decrypt('enx2:JKM3FFR4WP5HN6SG0C4ZAIF5K7H');
}