AFAIK, Impersonation means you want the application will run using a specific user credentials.
So your code will excute using the permissions or rights available to this specific user.
This has nothing to do with LLBLGen Pro, which uses a configuration setting for the database connection string. Which in turn can be using Integrated Security (to use the current user credentials to connect to the database) , rather than using a specific Database account.
So in fact LLBLGen Pro has nothing to do with deciding to use Impersonation or not, and it's not afected by this decision. It's merely a security design issue of your application.
(Edit)
Also I encourage you to search our forums for: Impersonation