Is it possible to use tensor flow in building an after effects plugin?

Yes, as @shachar carmi said, it should be possible, but with many challenges in practice.

If this should not only be an experiment that only runs on your machine, but something that you can distribute to others easily, it will be a big challenge to make sure users don't need to install the entire tensor flow. That probably means you want to use the Tensor Flow C API.

generally speking, there's no limit to what technologies can be used in an AE plugin. the plug-in is a DLL, written using a C API. besides the communications with AE bits that are srtictly done through the given C API, the DLL can do whatever it wants.

the only technical consideration is that AE can (and usially does) request frames to be rendered at random times and in random order. not all imaging technlogoies are fans of the notion... i have come across some video technologies that require generating the imag esequence in order, and either can't or can't efficiently handle random requests.

another consideratin might be performance. since AI tech usually makes intensive use of the GPU, loading and releasing it's entire data from from the GPU for each frame (as opposed to loading once, and then doing the whole process) might prove too time consuming to fit "comfortably" in the AE workflow.

there's also an issue of wide compatibility. not all AE users have graphics cards that are supported by AI libs. yes, a user can either use or not use your plug-in, but it might make his/her projects non-portable to other machines. not being able to run a project on any machine might prove problematic to some users. (most users, imho)

the one last thing i can think of the pollution... if the use of some infrastructure requires installing python and a bunhch of other tech on the user's machine as opposed to one neat folder in the plug-ins directory, not everyone would like that.