Can drives encrypted with Bitlocker be moved to different machines and accessed as long as the password is known? For example, via an external drive enclosure? Or is the encryption tied to the original computer?
Yes, provided you have the Key Protector (This may be a password, the Recovery Password, certificate, startup key, etc.) then you can access the encrypted drive from any machine which supports Bitlocker.
Usually if it's an internal drive it will be using either the TPM or a Startup Key, but will also generate a recovery password when you turn on Bitlocker. Windows will prompt for the password when you connect the drive to another computer.
External (removable) drives usually use a user-provided password + generated recovery password.
A BitLocker encrypted volume is not tied to the original computer in any way.