Yes, but no. No, in that these days, GPUs are entirely scalar from the point of view of invocations. Using vectors in shaders is pointless - it will be as fast as scalar variables (double instruction dispatch on AMD GPUs is an exception).

But yes from the point of view that a collection of invocations all progressing in lockstep get arithmetic done by vector units. GPUs have just gotten really good at hiding what happens with branching paths between invocations.