Jake,
You don?t ?necessarily? have to renumber all your admin DNs; however, it is strongly, strongly suggested for the following reason: In your route plan, all your internal #s will not provide dial tone after a caller hits the first ?8? on the key pad, but when they hit ?8? for an outside line and use route pattern?8?.XXX-XXXX, they won?t receive secondary dial tone until they?re half-way through the number (if you?re using 4-digit DNs). This would freak most phone users out.
The other problem would be if they dial an outside number 8.1234567, if you have an IP phone with 8123, it will call the phone first.
These would be your two biggest problems that would motivate you to renumber everything else, or perhaps use "7" as the outside access code.