Recently watched the eairler eqisodes and you'r right about that part. His jacket looks too much like a marine captains jacket, tho with the lighting it still could have been one. Plus if you take whats happened to Jango it could quite easy be another of Kuro's plans to get back at Luffy.Marine? Seriously? I remember him just being on his old ship sitting in his cabin over the bounty. Nothing about being a marine.
And to the earlier question about Kuro knowing soru, he doesn't. This is because he uses flash steeps which is just him buliding up speed similar to the dash of soru but still not the same. All you have to do is look at the results to see the difference in technique.