If you're actually running FM on a Windows server platform, then there's a high probability that the EULA demands you use the FrameMaker Publishing Server (FPS) instead. However, if you're just accessing existing FM files and not triggering FM via Webworks to do anything, then I don't see how a FPS license would be required.
There's a bit of info on the differences in the licenses at: FAQ | FrameMaker Publishing Server 12
However, I can't seem to find any more recent versions of the EULAs than the FM11 and FPS10 ones listed here: Licenses and terms of use | Adobe