Yes. A device can have many different provisions installed from many different developers, either or both enterprise and personal (or occasionally special ones from Apple).
In summary, when you sign up for and are accepted into a paid iOS developer program, you can create and download 2 certificates, then you can download provisions (using those certificates and your device UDIDs and your app IDs), then Xcode, using those certificates and provisions, can build and sign apps that will run on any devices with those UDIDs and with those provisions installed.
