As written in the header: Studio One chases dynamics roughly with Velocity based instruments like piano, and in this case only the fixed dynamics like p and f, but hairpins are ignored. Also, in orchestral VST's, dynamics are handled by changing CC values, most of the time eiter CC1 or CC11, so you can also make gradual dynamic changes.
Unfortunately S1 doesn't have any option to make this work. It would be great if in the next update (or version), this could be implemented. Recording dynamics afterwards, or drawing them in, is very time consuming and a clunky way to get the same result. Cubase does this pretty well, but I highly prefer S1 over Cubase as it feels much more intuitive and all those floating windows are gone. This, plus the score editor in S1 which is miles ahead of the Cubase version, but not being able to use written dynamics to play the score back properly is a downer for me.