Can X-Plane be used as a professional simulator?
Maybe.

From the page linked by falstro above:


  These include the ability to use cylindrical and spherical projection (as found in large simulators), and the ability to drive real Garmin 1000, Garmin 430, Garmin 430 WAAS, Garmin 530, and Garmin 530 WAAS units.


Pictures are included of a particular setup. The large projection format allows all-around visuals. The simulator can drive real Garmin devices, not just replicas. They recommend this vendor for FAA approved hardware (and for $2,100 I would hope a yoke could be FAA certified).

You can use an IOS even with the personal license for the simulator, on the same computer or a separate one.

X-Plane also explains that only the complete hardware+software combination can be certified for use as an FAA approved flight simulator. So it may be easier to just buy a package from a company like PFC, which has the combination already certified. They offer BATD and AATD simulator setups that use X-Plane.

If you need more information, you can contact X-Plane via the link on the same site linked above. They do not keep track of what people use their professional licenses for, but they may be able to comment on what level of certification is achievable.