If I dual boot my work computer and set the hostname to the same as it is in Windows (so that there is already an entry for the computer in Active Directory), should I be able to join the work domain by just using my Windows domain login credentials?
Or do I need to have an admin set up my PC to be on the domain first?
No, because the ways in which Windows and Linux handle passwords is different, no to mention that Windows and Linux encode passwords differently.
If you install Samba 4 you can have all the features of Active Directory on your Linux machine including a program which allows you to generate and use Windows passwords on Linux.
You will need to set this up as Admin but you don’t need to use it as Admin - it is better that you do not.