I think you are referring to two different species of Seriatopora. S. guttatus has bushier polyps and isn't as thin branching as Seriatopora hystrix. So, they are in the same genus, but are different species.
Differences in flow will surely effect the way individuals mature. As Seriatopora colonies become more dense, they require more flow to compensate for the increase in mass. If they don't receive adequate flow then coloration and growth will be affected. With a small frag, moderate flow and lighting (trending towards lower flow for S. guttatus) has worked well for me in numerous situations.