They could. However, the usual practice is to wrap any structural member (wood, concrete block, steel) with felt or roofing paper to keep any moisture from condensation on steel — or moisture that might be drawn out of the plaster or stucco or concrete — away from the straw. A moisture barrier such as plastic probably isn't the best solution for wrapping the structural members because moisture also tends to condense and collect on it.

Straw bale construction is based on the age-old practice of building with what you have at hand. Concrete-block columns have been used as structural elements in straw bale buildings. They’re often chosen because the blocks can be readily found or salvaged, or can be purchased at an affordable cost.