Is the “loosh” described by Robert Monroe as our spiritual energy that is sought by non-physical beings, especially dark spirits, a useful concept? Is that identical to “life force energy,” being neutral, the energy supplied from the divine that keeps us alive?

That is its origin, the life-force energy. So loosh is a portion of life force energy that has a darker character, a darker quality in the frequency as a consequence of human experiencing and altering the energetic frequency accordingly, by thoughts and feelings of a darker sort. So this changes the energy into a form that is an expression of negativity and as such is not in divine alignment and makes it a much better match to the dark spirits, their energy level, and their way of thinking. So it is particularly desirable to them because it is readily used, as it fits right in. So it is much like alcohol to one who is addicted. It is what they crave, and what they have come to depend on and feel they need.