So, our team has an immersion lifestyle hacker on it. The player actually lives in another state and we use Google+ circle or whatever its called to have him on the line as we play.

The GM seems to be of the mind that he can't hack anything not within mutual signal range of him personally without having a repeater drone floating around while I contend that as long as he is subscribed to either our ninja's commlink or my head (my character is a TM Rigger) he can use that as his endpoint for determining mutual signal range. Anyone have any crunch references to prove it one way or the other?

Pg 224 in SR4A under Subscriptions. By the way, you're interpretation is right. The only caveat is that your hacker has to be subscribed to your link (using one of his subscriptions) and you of course, must be within mutual signal range of the node he wants to hack. Keep in mind, all wireless devices work as routers in SR so a dedicated retrans unit is not needed unless you are in a matrix free zone (the middle of the Arctic for example)