Based on this question on the big meta.
Source Filmmaker is a video editing program built on the Source game engine. This makes it related to our site, but not definitively on topic. So, should we allow these questions?
No, questions about creating videos, such as those made using Source Filmmaker should be asked on the Video Production Stack Exchange.
The list of potential on topics (It is listed as a 'Such As' not meant to be an all inclusive)
None of these work for me as making this on topic. Again the list above is just guidelines for what to consider. But if making a minecraft video in Maya is not on topic as well for us then I do not see how using SFM to make a video with DotA2 characters as on topic.
The list of definitely off topic topics also does not apply here. It simply just is not on either list.
The last point is that there is a question about the use of SFM on the SE sites already. As pointed out yesterday in discussion, there is no rule stating questions can only be on topic for one SE site.
However, the question over on SU is the exact same problem with one minor difference. The user is unable to get an asset file to load into SFM. In that case it is an Audio file. In the case of the question that came up to start this discussion it was a level from DotA2. The case seems to be that because someone is using assets from a game that it is on topic for us. I again take the stance as above that if we do not open this up to use any piece of software that is making use of assets created for a game, then this remains off topic.
Source Film Maker is a video editor. It's not specific to one game. Any model that works in the Source engine can be used in it.
The Source Developer wiki has plugins that can be used with software like Softimage Mod Tool (now discontinued), Maya, Blender, or Milkshape 3D to export to Source's SMD or DMX formats. That file is used with
studiomodel.exe with a QC file to create a compiled MDL file which can then be used in Source Film Maker.
Why point out the above? Because it makes it clear that any model can be used with it.