Are spiritual vibrations ACTUAL vibrations, or is the term used metaphorically?
The short answer is YES! They are actual not metaphorical.
Everything that exists within creation is vibrating. Every atom, every ray of energy of any type, and even every thought.
The great Masters of Yoga say that the material or physical world is only one of three, the other two being the astral world (energy) and the causal world (thought). All three have communication with and influence on each other.
But all three still exist within creation. Beyond creation is an un-moving, un-vibrating Presence which is the Creator.
This Creator (God) beyond creation brought everything into existence through the power of vibrations. And there is a spark of that Divine Creative Energy within all creation.
So in that sense, everything that exists is vibrating with a spiritual vibration (the "God-spark" within us and in all creation, energy, thought, etc).
Perhaps you might call this a "spiritual vibration." It is very real (actual) to all who have experienced it.
Our destiny is to go beyond all vibration, all creation, and the three planes of existence and return to oneness with our Creator beyond all creation.
Yoga, its deepest meaning, means union with our Creator, beyond all vibrations.