Teleporting and Body Flickering are two different things.
Teleporting is the act of disappearing from one spot into another, without going into the space between them. Meaning that Minato, Tobirama, and Obito could stand in a room with a locked door and no windows, and use FTG or Kamui without somehow busting through the door or the walls. They literally do not fill the space in between their starting point and their destination.
If the area where the Susano'o user stands is indeed hollow, then it would be possible for the user of FTG to appear in the same area with the user of Susano'o. Because of the many movements seen by users of Susano'o WHILE in Susano'o, it can be concluded that those who stay on the ground are in a giant hollow space that could easily fit Minato or Tobirama. The user of Susano'o just seems to move Susano'o with them as they move, likely requiring a conscious effort.
However, if the user can fill extra space with chakra, which has not been shown yet, then he has not allowed a space for the FTG user to be in.
So, until proven otherwise, I believe that a FTG user can teleport inside of Susano'o if his opponent were to be marked.