Same rules apply for any item from another simulator, Possible, yes, Practical no. Unless you have permission from the creator / owner of the item and can obtain the original mesh, that's the 3d model as created in Gmax, Blender, 3ds or whatever program they use before it has been exported then it isn't going to happen.
It's highly unlikely that anyone other than a skilled and well known creator in both camps would even get permission. Just having a model in Railworks or MSTS is of no use for Trainz without the original mesh and even then due to the different requirements and techniques used in different simulators it may not be possible without rebuilding parts and re-texturing. May as well start from scratch.