I was told by Slingbox technical staff that when you view video from inside your network, the video is streamed from the Slingbox.
I have my Slingbox connected in the basement to a wired connection. However, I view from my Windows and Mac laptops that are connected wirelessly to the network. No worries there.
You mentioned that the Slingbox is connected to the wireless router. If the Mac connect wirelessly to the nework you may be just fine. It won't hurt to try it out. If you have a Slinbox Pro HD, you will need to use Safari on the Mac to view the video. If you have a Slingbox or Slingbox SOLO, you can try out the Mac client. The Windows client is free, the Mac client probably too.