No, they are probably using evanescent wave technology. Fiber optics works by reflecting the light down a channel - when light hits an interface between media with two different speed of lights, there is a reflective component and a refractive component. If you solve snell's law for a very shallow beam hitting a less dense media, you get an imaginary value for the angle of the refractive component. One way to interpret this is that zero of the light energy is reflected. But if you solve a wave function cos(x) with an complex value x, that is equivalent to a function with a complex exponential, potentially with nonzero, real preexponential.

That is what an evanescent wave is. There is light that decays exponentially "bleeding" off the reflective surface[1]. The snell's law solution is sort of a hack, what is really going on has to do with the quantum wavefunction of the photon ensembles, but the result is the same.

Biologists use evanescent waves to do microscopy - you can illuminate an area of low density underneath your coverslip, and effectively a very very thin layer of flourescence is illuminated right above the coverslip.

It would seem reasonable that the NSA would use exactly this technology to tap fiber optic cables without splicing them, and it should be nearly undetectable. There will be a nonzero loss of photons if you tap it, but it should be relatively negligible.

[1]note - the photonic energy is just 'there' as in the wavefunction has nonzero amplitude in that spatial region. It's 'bleeding' into the space outside of the fiber optic channel, but it's not actually bleeding energy, there is no energy loss from this 'spatial bleeding', unless there is something in that zone that is capable of absorbing that photonic energy.