Answer:
Generally speaking, manufactured diamonds have the same chemical and physical properties of diamonds which are dug from the earth. So, yes, they are real. A certified gemologist will be able to discern a manufactured diamond, and will document it as such. Its value is considerably less than a natural diamond of similar characteristics.
Manufactured diamonds are not natural diamonds. There are other man-made gemsones which are presented as diamond substitutes. Those are not real diamonds either.