Is it possible to use FileVault 2 on a non-primary boot partition? (Dual-boot setup)
Yes, this should work fine. I actually have essentially this config on one of my computers , the only odd thing is that my default boot (unencrypted) is OS X 10.8 (Mountain Lion), and the alternate (encrypted) partition is OS X 10.9 (Mavericks). I'm not really using it in this mode (it's a test computer that just happened to wind up with this combo), but the only unusual thing I've noticed is that when you boot from the unencrypted partition, every time you log in it asks you to unlock the encrypted partition so it can be mounted. You can either enter the password of one of the FileVault-enabled accounts from the encrypted partition, or click Cancel and go about your business.

I do not have a firmware password set on this test computer, but I wouldn't expect setting one to cause any problem. To boot from the encrypted partition, you'd have to start the computer with the Option key held down, enter the firmware password, select the alternate partition, then enter one of the FileVault-enabled account passwords. After that, it should behave normally.