Interesting theory, but I doubt that Miles is Chang's son. I have a few superficial reasons for it, none really excellent.
1) Pierre Chang and Miles Straume have different last names. Not big, I know.
2) Pierre is a french name. Miles isn't. Also not big at all.
3) Miles seems to not be the right age to be Pierre's son, but I suppose it's possible.
4) Wasn't there something about pregnancies on the island? hm...
BUT
5) Pierre and Miles have different specialties. Pierre deals mostly with time physics while Miles deals with parapsychology. I would expect that Pierre's son would be more interested in the physics than the psychology.
6) Why would Miles have left the island? OR Why would Miles not have been brought to the island sooner?
Miles would've left the island because Chang was warned by Daniel's coming back about the upcoming Purge. He wanted his son out of it even if he himself was doomed, so he somehow sent him off-island. At least, that's what I would do. So if that's it, then Miles grew up off-island raised by someone else (maybe named Straume.) And maybe the name-change was for his own protection -- Chang didn't want anybody tracking him down, so he arranged for an adoption and name-change. Again, that's probably what I would do.
I would say the age is about right, isn't it? Isn't Miles around 30, give or take? And Dr. Chang's Barracks Video (with the baby crying in the background) says it will be seen "about 30 years" in the future.
I have no idea when the problems with island pregnancies started. My guess is post-Purge, because Dharma seemed like it was rolling along pretty smoothly there for awhile, with schools and school-age kids (some of whom could've come to the island like young Ben did, but probably not all?) Either way, Miles could've been conceived off-island.
Anyway, just some thoughts.