I had to add the VS2013 paths in my user profile for "Path":
C:\Program Files (x86)\Microsoft Visual Studio 12.0\Common7\IDE\;C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\BIN;C:\Program Files (x86)\Microsoft Visual Studio 12.0\Common7\Tools;
This appears to fix CUDAfy viewer (with the known exception for math libraries) :
Checking for CUDA SDK at C:\Program Files\NVIDIA GPU Computing Toolkit\CUDA\v6.5\bin\nvcc
CUDA SDK Version=6.5
Attempting to cudafy a kernel function.
Successfully translated to CUDA C.
Attempting to compile CUDA C code.
Successfully compiled CUDA C into a module.
Attempting to instantiate CUDA device object (GPGPU).
Successfully got CUDA device 0.
Attempting to load module.
Successfully loaded module.
Attempting to transfer data to GPU.
Successfully transferred data to GPU.
Attempting to launch function on GPU.
Successfully launched function on GPU.
Attempting to transfer results back from GPU.
Successfully transferred results from GPU.
Successfully tested results.
Checking for math libraries (FFT, BLAS, SPARSE, RAND).
Unable to load DLL 'cufft64_60': The specified module could not be found. (Exception from HRESULT: 0x8007007E)