Why has he had dreams of abduction experiences and seeing a Reptilian-type being?

These are not dreams but dreams about actual events being recalled as a memory. It was, in effect, a replay of actual occurrences. This is because he is under watch from them and is being manipulated directly at times because he is of interest in studying his genetic makeup, so he is given physical examinations to monitor things they are doing over the generations and wish to compare how things are going relative to past checkups. He is not a member of the Mercenary Army Program, which is a blessing, but only a subject for scientific study to serve the aims of the alien Greys.