From everything I've read, it might be possible, but you will have to do some serious hoop jumping to make it work. To use Boot Camp, you must install on the primary drive in the portable computer, and you must install from the internal optical drive if the system shipped with one. That would mean that you would not be able to have the SSD in the optical bay when you install Windows 8, but it does not mean that you can't install Windows before you put the SSD in the optical bay.
As a side note, depending upon which MacBook Pro model you have, putting an SSD in the optical bay is not a wise choice. Some models have issues with the SATA link negotiation process, and in some models, the drive is "logically disconnected" at random times, which would not be good if you are using the drive as your boot drive.