WIll an Olympus TCON-17X teleconverter work on a Fujifilm X100 series camera?

The only way to know what will happen is to try it. As you state, "the connection should be no problem", just use a 49-55 step-up ring. However, the lens is 23mm, so the ring may be visible along the edges of the frame.

Step-up rings are fairly inexpensive, so if you already have the adapter and converter, you can go ahead and try it. Otherwise, consider you'll likely have a much better experience by using FujiFilm's native converters:

• Wide Conversion Lens WCL-X100 II - 0.8×, 23mm → 19 mm
• Tele Conversion Lens TCL-X100 II - 1.4×, 23mm → 33 mm