Using molasses through flushing is perfectly acceptable, and in fact good.
Here is a little general info about different types of molasses.
Organic vs. Commercial "Not-Organic" Molasses
Many batches of organic blackstrap can give you a bit of a hard time if you are shooting for a very rapid pH drop. This is because organic blackstrap molasses contains even more calcium and other ionic minerals than does "inorganic" blackstrap, and the calcium and other mineral ions act as massive buffers against pH drop, thus slowing the pH drop considerably. So, if your goal is rapid pH drop upon starting fermentation, go with the not-organic versions; they will usually be lower in Ca and other minerals, due to the refining/squeezing processes used (and perhaps partially due to soil quality/mineral content as well).
Other Kinds of Molasses and other Sweeteners
It does appear to be possible to use other sugars to feed the EM organisms in brewing, and this successfully been done. However, the major problem which arises with simple using sugars (such as dextrose, fructose, corn syrup, honey, mannitol, etc.) is that they do not offer any complex sugars or complex carbohydrates, nor do they offer any minerals or trace minerals as feed for the "bugs", and so, if using a simple sugar, you would need to add a bit of sea salt, some minerals and maybe even some source of complex sugars.