Yeah, the only Sector that's limited by your Marauder level is the Sirius Sector Block That you need Level 3 (or Raiding Party applied to you from someone else) to enter. But you still can't enter Earth Spacedock, or the Sol System.
And vice-versa on the Fed side, in regards to our own Sector Block.
If you are thinking you cannot get to it as the entry is in Sirius sector block, you are right you need Marauding 4 to go that way. Fortunately you can go and kill, ahem rescue, a few Deferi in Orellius sector block on the way through their sector and come in the back door route.