Yes friend, you can do it on FPS Creator, you can use motion capture the same way you use in any other engine.
The thing you must understand is about the animation system on FPSC.
You can even have custom animations for FPS Creator, however, is better, less problem, if you follow the same FPSC animation template (run, walk, shoot, reload, and such).
If you want to have new animations, you must specify them through scripting. It`s a good idea you study the official community guide to FPSC, to have a geral understanding on FPI Scripting.
I have done this, using MOCAP (those packages that you purchase over the internet), to create "flinch" (impact) animations for my characters.
You can even use mocap for death animations, however, now FPSC supports ragdoll animation, so there is no need to have custom death animations.
You can even use MOCAP for walking, running, and such. However, the problem is that you must create a "walkcycle", where the last frame of the animation is exactly equal the first frame, to avoid having "flickering" on the movement.
For this, the best workflow you can use is to do the MOCAP with Kinect Sensors, then import the data to Motion Builder, in motion builder you edit the character animation, create the walkcycle, in example, then you import the fbx file (model and animation) in 3dsmax, then export to DirectX Format using the Pandasoft X File exporter.
Its not hard, however, you need to do a lot of work and you need to create those movement cycles (running cycle, walking cycle, and such) to ensure that you will have a smooth movement for your FPSC characters.
Cheers,
007.
Goldenye 007 N64