Yes, you login to your Square Enix Account on all platforms, so your character's information is available from any of them. This includes what server you are on. The only conditions that are a detriment to playing on multiple platforms is that currently, any macro, hotbar, or Gear Set settings are not saved across platforms. In other words, they are stored locally on your machine, so you need to re-do, or update them. This is in the works to be changed down the line, but it doesn't really stop you from playing, just an inconvenience.