It depends on what the application is for.
First of all an application that is signed with an enterprise distribution profile can be used only for internal usage of the signing enterprise!!!
Assuming that the above is true then the app should be signed with CPG profile, and if the contract employees are permitted by CPG to do internal work for CPG then they can use the app.
If the scenario is different and you are building a more generic app that has the same base code and can be used by different enterprises for different purposes and you want to control distribution per enterprise then I suggest to use the B2B distribution where you can distribute variations of the same base code to different enterprises and it has a lot of benefits like the distribution is using the apple AppStore distribution infrastructure and the signing is with the AppStore account...
If you want more details about who can use enterprise app then I would suggest to read the license agreement, it's all in there.
Hope it helps.