I think it's important to note that Symantec Drive Encryption (solely the Drive Encryption portion of the product) does not require the use of PGP keys. If the user is using other key based encryption features (such as Messaging, PGP zip, File Share Encryption, etc.) Then they would need to go through the key generation wizard. If you give users the option to do this via policy on the Symantec Encryption Management Server. They can simply open up Symantec Encryption Desktop and select the option in the toolbar as:
File --> New PGP Key
If that option is not available on the managed client. Then you need to enable the option via Consumer Policy to allow users to generate keys.